Allocates blocks for files ending un-PG-aligned

[akaros.git] / kern / src / ext2fs.c

/* Copyright (c) 2010 The Regents of the University of California
 * Barret Rhoden <brho@cs.berkeley.edu>
 * See LICENSE for details.
 *
 * Ext2, VFS required functions, internal functions, life, the universe, and
 * everything! */

#include <vfs.h>
#include <ext2fs.h>
#include <blockdev.h>
#include <kmalloc.h>
#include <assert.h>
#include <kref.h>
#include <endian.h>
#include <error.h>
#include <pmap.h>
#include <arch/bitmask.h>

/* These structs are declared again and initialized farther down */
struct page_map_operations ext2_pm_op;
struct super_operations ext2_s_op;
struct inode_operations ext2_i_op;
struct dentry_operations ext2_d_op;
struct file_operations ext2_f_op_file;
struct file_operations ext2_f_op_dir;
struct file_operations ext2_f_op_sym;

/* EXT2 Internal Functions */

/* Useful helper functions. */

/* Returns the block group ID of the BG containing the inode.  BGs start with 0,
 * inodes are indexed starting at 1. */
static struct ext2_block_group *ext2_inode2bg(struct inode *inode)
{
        struct ext2_sb_info *e2sbi = (struct ext2_sb_info*)inode->i_sb->s_fs_info;
        unsigned int bg_num = (inode->i_ino - 1) /
                              le32_to_cpu(e2sbi->e2sb->s_inodes_per_group);
        return &e2sbi->e2bg[bg_num];
}

/* This returns the inode's 0-index within a block group */
static unsigned int ext2_inode2bgidx(struct inode *inode)
{
        struct ext2_sb_info *e2sbi = (struct ext2_sb_info*)inode->i_sb->s_fs_info;
        return (inode->i_ino - 1) % le32_to_cpu(e2sbi->e2sb->s_inodes_per_group);
}

/* Returns an uncounted reference to the BG in the BG table, which is pinned,
 * hanging off the sb.  Note, the BGs cover the blocks starting from the first
 * data block, not from 0.  So if the FDB is 1, BG 0 covers 1 through 1024, and
 * not 0 through 1023. */
static struct ext2_block_group *ext2_block2bg(struct super_block *sb,
                                              uint32_t blk_num)
{
        struct ext2_sb_info *e2sbi = (struct ext2_sb_info*)sb->s_fs_info;
        unsigned int bg_num;
        bg_num = (blk_num - le32_to_cpu(e2sbi->e2sb->s_first_data_block)) /
                 le32_to_cpu(e2sbi->e2sb->s_blocks_per_group);
        return &e2sbi->e2bg[bg_num];
}

/* This returns the block's 0-index within a block group.  Note all blocks are
 * offset by FDB when dealing with BG membership. */
static unsigned int ext2_block2bgidx(struct super_block *sb, uint32_t blk_num)
{
        struct ext2_sb_info *e2sbi = (struct ext2_sb_info*)sb->s_fs_info;
        return (blk_num - le32_to_cpu(e2sbi->e2sb->s_first_data_block)) %
               le32_to_cpu(e2sbi->e2sb->s_blocks_per_group);
}

/* Returns the FS block for the given BG's idx block */
static uint32_t ext2_bgidx2block(struct super_block *sb,
                                 struct ext2_block_group *bg,
                                 unsigned int blk_idx)
{
        struct ext2_sb_info *e2sbi = (struct ext2_sb_info*)sb->s_fs_info;
        struct ext2_sb *e2sb = e2sbi->e2sb;
        struct ext2_block_group *e2bg = e2sbi->e2bg;
        return (bg - e2bg) * le32_to_cpu(e2sb->s_blocks_per_group) + blk_idx +
               le32_to_cpu(e2sb->s_first_data_block);
}

/* Slabs for ext2 specific info chunks */
struct kmem_cache *ext2_i_kcache;

/* One-time init for all ext2 instances */
void ext2_init(void)
{
        ext2_i_kcache = kmem_cache_create("ext2_i_info", sizeof(struct ext2_i_info),
                                          __alignof__(struct ext2_i_info), 0, 0, 0);
}

/* Block management */

/* Helper op to read one ext2 block, 0-indexing the block numbers.  Kfree your
 * answer.
 *
 * TODO: consider taking a buffer_head, or having a generic block_dev function
 * for this.  Currently this is just using the BH to talk to breq, need to make
 * it use the page mapping. */
void *__ext2_read_block(struct block_device *bdev, int block_num, int blocksize)
{
        int retval;
        void *buffer = kmalloc(blocksize, 0);
        struct block_request *breq = kmem_cache_alloc(breq_kcache, 0);
        struct buffer_head *bh = kmem_cache_alloc(bh_kcache, 0);
        assert(buffer && breq && bh);

        /* Build the BH describing the mapping we want */
        bh->bh_buffer = buffer; // TODO: have a real page
        bh->bh_sector = block_num * (blocksize >> SECTOR_SZ_LOG);
        bh->bh_nr_sector = blocksize >> SECTOR_SZ_LOG;
        /* Build and submit the request */
        breq->flags = BREQ_READ;
        breq->bhs = breq->local_bhs;
        breq->bhs[0] = bh;
        breq->nr_bhs = 1;
        retval = make_request(bdev, breq);
        assert(!retval);
        kmem_cache_free(breq_kcache, breq);
        kmem_cache_free(bh_kcache, bh); /* TODO: shouldn't disconnect this */
        return buffer;
}

/* TODO: pull these metablock functions out of ext2 */
/* Makes sure the FS block of metadata is in memory.  This returns a pointer to
 * the beginning of the requested block.  Release it with put_metablock().
 * Internally, the kreffing is done on the page. */
void *__ext2_get_metablock(struct block_device *bdev, unsigned long blk_num,
                           unsigned int blk_sz)
{
        struct page *page;
        struct page_map *pm = &bdev->b_pm;
        unsigned int blk_per_pg = PGSIZE / blk_sz;
        unsigned int blk_offset = (blk_num % blk_per_pg) * blk_sz;
        int error;
        assert(blk_offset < PGSIZE);
        error = pm_load_page(pm, blk_num / blk_per_pg, &page); 
        if (error) {
                warn("Failed to read metablock! (%d)", error);
                return 0;
        }
        /* return where we are within the page for the given block */
        return page2kva(page) + blk_offset;
}

/* Convenience wrapper */
void *ext2_get_metablock(struct super_block *sb, unsigned long block_num)
{
        return __ext2_get_metablock(sb->s_bdev, block_num, sb->s_blocksize);
}

/* Decrefs the buffer from get_metablock().  Call this when you no longer
 * reference your metadata block/buffer */
void ext2_put_metablock(void *buffer)
{
        page_decref(kva2page(buffer));
}

/* Will dirty the block/BH/page for the given metadata block/buffer.  Will have
 * to be careful with the page reclaimer - if someone holds a reference, they
 * can still dirty it. */
void ext2_dirty_metablock(void *buffer)
{
        struct page *page = kva2page(buffer);
        /* TODO: race on flag modification, and consider dirtying the BH. */
        page->pg_flags |= PG_DIRTY;
}

/* Reads a block of file data.  TODO: Function name and guts will change soon */
void *ext2_read_fileblock(struct super_block *sb, unsigned int block_num)
{
        /* note, we might get rid of this read block, if all files use pages */
        return __ext2_read_block(sb->s_bdev, block_num, sb->s_blocksize);
}

/* Helper for alloc_block.  It will try to alloc a block from the BG, starting
 * with blk_idx (relative number within the BG).   If successful, it will return
 * the FS block number via *block_num.  TODO: concurrency protection */
static bool ext2_tryalloc(struct super_block *sb, struct ext2_block_group *bg,
                          unsigned int blk_idx, uint32_t *block_num)
{
        uint8_t *blk_bitmap;
        struct ext2_sb_info *e2sbi = (struct ext2_sb_info*)sb->s_fs_info;
        unsigned int blks_per_bg = le32_to_cpu(e2sbi->e2sb->s_blocks_per_group);
        bool found = FALSE;

        /* Check to see if there are any free blocks */
        if (!le32_to_cpu(bg->bg_free_blocks_cnt))
                return FALSE;
        /* Check the bitmap for your desired block.  We'll loop through the whole
         * BG, starting with the one we want first. */
        blk_bitmap = ext2_get_metablock(sb, bg->bg_block_bitmap);
        for (int i = 0; i < blks_per_bg; i++) {
                if (!(GET_BITMASK_BIT(blk_bitmap, blk_idx))) {
                        SET_BITMASK_BIT(blk_bitmap, blk_idx);
                        bg->bg_free_blocks_cnt--;
                        ext2_dirty_metablock(blk_bitmap);
                        found = TRUE;
                        break;
                }
                /* Note: the wrap-around hasn't been tested yet */
                blk_idx = (blk_idx + 1) % blks_per_bg;
        }
        ext2_put_metablock(blk_bitmap);
        if (found)
                *block_num = ext2_bgidx2block(sb, bg, blk_idx);
        return found;
}

/* This allocates a fresh block for the inode, preferably 'fetish' (name
 * courtesy of L.F.), returning the FS block number that's been allocated.
 * Note, Linux does some block preallocation here.  Consider doing the same (off
 * the in-memory inode).  Note the lack of concurrency protections here. */
uint32_t ext2_alloc_block(struct inode *inode, uint32_t fetish)
{
        struct ext2_sb_info *e2sbi = (struct ext2_sb_info*)inode->i_sb->s_fs_info;
        struct ext2_block_group *fetish_bg, *bg_i = e2sbi->e2bg;
        unsigned int blk_idx;
        uint8_t *blk_bitmap;
        bool found = FALSE;
        uint32_t retval = 0;

        /* Get our ideal starting point */
        fetish_bg = ext2_block2bg(inode->i_sb, fetish);
        blk_idx = ext2_block2bgidx(inode->i_sb, fetish);
        /* Try to find a free block in the BG of the one we desire */
        found = ext2_tryalloc(inode->i_sb, fetish_bg, blk_idx, &retval);
        if (found)
                return retval;

        warn("This part hasn't been tested yet.");
        /* Find a block anywhere else (perhaps using the log trick, but for now just
         * linearly scanning). */
        for (int i = 0; i < e2sbi->nr_bgs; i++, bg_i++) {
                if (bg_i == fetish_bg)
                        continue;
                found = ext2_tryalloc(inode->i_sb, bg_i, 0, &retval);
                if (found)
                        break;
        }
        if (!found)
                panic("Ran out of blocks! (probably a bug)");
        return retval;
}

/* Inode Table Management */

/* Helper for ino table management.  blkid is the inode table block we are
 * looking in, rel_blkid is the block we want, relative to the current
 * threshhold for a level of indirection, and reach is how many items a given
 * slot indexes.  Returns a pointer to the slot for the given block. */
static uint32_t *ext2_find_inotable_slot(struct inode *inode, uint32_t blkid,
                                         uint32_t rel_blkid,
                                         unsigned int reach)
{
        uint32_t *blk_buf = ext2_get_metablock(inode->i_sb, blkid);
        assert(blk_buf);
        return &blk_buf[rel_blkid / reach];
}

/* If blk_slot is empty (no block mapped there) it will alloc and link a new
 * block.  This is only used for allocating a block to be an indirect table
 * (it's grabbing a metablock, we have no hint, and it handles the buffer
 * differently than for a file page/buffer). */
static void ext2_fill_inotable_slot(struct inode *inode, uint32_t *blk_slot)
{
        uint32_t new_blkid, hint_blk;
        void *new_blk;

        if (le32_to_cpu(*blk_slot))
                return;
        /* Use any block in our inode's BG as a hint for the indirect block */
        hint_blk = ext2_bgidx2block(inode->i_sb, ext2_inode2bg(inode), 0);
        new_blkid = ext2_alloc_block(inode, hint_blk);
        /* Actually read in the block we alloc'd */
        new_blk = ext2_get_metablock(inode->i_sb, new_blkid);
        memset(new_blk, 0, inode->i_sb->s_blocksize);
        ext2_dirty_metablock(new_blk);
        /* We put it, despite it getting relooked up in the next walk */
        ext2_put_metablock(new_blk);
        /* Now write the new block into its slot */
        *blk_slot = cpu_to_le32(new_blkid);
        ext2_dirty_metablock(blk_slot);
}

/* This walks a table stored at block 'blkid', returning which block you should
 * walk next in 'blkid'.  rel_inoblk is where you are given the current level of
 * indirection tables, and returns where you should be for the next one.  Reach
 * is how many items the current table's *items* can index (so if we're on a
 * 3x indir block, reach should be for the doubly-indirect entries, and
 * rel_inoblk will tell you where within that double block you want).
 *
 * This will also alloc intermediate tables if there isn't one already (TODO:
 * concurrency protection on modifying the table). */
static void ext2_walk_inotable(struct inode *inode, uint32_t *blkid,
                               uint32_t *rel_inoblk, unsigned int reach)
{
        uint32_t *blk_slot;
        blk_slot = ext2_find_inotable_slot(inode, *blkid, *rel_inoblk, reach);
        /* We could only do this based on a bool, but if we're trying to walk it,
         * we ought to want to alloc if there is no block. */
        ext2_fill_inotable_slot(inode, blk_slot);
        *blkid = le32_to_cpu(*blk_slot);
        *rel_inoblk = *rel_inoblk % reach;
        ext2_put_metablock(blk_slot);   /* the ref for the block we looked in */
}

/* Finds the slot of the FS block corresponding to a specific block number of an
 * inode.  It does this by walking the inode's tables.  The general idea is that
 * if the ino_block num is above a threshold, we'll need to go into indirect
 * tables (1x, 2x, or 3x (triply indirect) tables).  Block numbers start at 0.
 *
 * This returns a pointer within a metablock, which needs to be decref'd (and
 * possibly dirtied) when you are done.
 *
 * Horrendously untested, btw. */
uint32_t *ext2_lookup_inotable_slot(struct inode *inode, uint32_t ino_block)
{
        struct ext2_i_info *e2ii = (struct ext2_i_info*)inode->i_fs_info;

        uint32_t blkid, *blk_slot;
        /* The 'reach' is how many blocks a given table can 'address' */
        int ptrs_per_blk = inode->i_sb->s_blocksize / sizeof(uint32_t);
        int reach_1xblk = ptrs_per_blk;
        int reach_2xblk = ptrs_per_blk * ptrs_per_blk;
        /* thresholds are the first blocks that require a level of indirection */
        int single_threshold = 12;
        int double_threshold = single_threshold + reach_1xblk;
        int triple_threshold = double_threshold + reach_2xblk;
        /* this is the desired block num lookup within a level of indirection.  It
         * will need to be offset based on what level of lookups we want (try it in
         * your head with 12 first). */
        uint32_t rel_inoblk;

        if (ino_block >= triple_threshold) {
                /* ino_block requires a triply-indirect lookup */
                rel_inoblk = ino_block - triple_threshold;
                /* Make sure a 14 block (3x indirect) is there */
                ext2_fill_inotable_slot(inode, &e2ii->i_block[14]);
                blkid = e2ii->i_block[14];
                ext2_walk_inotable(inode, &blkid, &rel_inoblk, reach_2xblk);
                ext2_walk_inotable(inode, &blkid, &rel_inoblk, reach_1xblk);
                blk_slot = ext2_find_inotable_slot(inode, blkid, rel_inoblk, 1);
        } else if (ino_block >= double_threshold) {
                /* ino_block requires a doubly-indirect lookup  */
                rel_inoblk = ino_block - double_threshold;
                ext2_fill_inotable_slot(inode, &e2ii->i_block[13]);
                blkid = e2ii->i_block[13];
                ext2_walk_inotable(inode, &blkid, &rel_inoblk, reach_1xblk);
                blk_slot = ext2_find_inotable_slot(inode, blkid, rel_inoblk, 1);
        } else if (ino_block >= single_threshold) {
                /* ino_block requires a singly-indirect lookup */
                rel_inoblk = ino_block - single_threshold;
                ext2_fill_inotable_slot(inode, &e2ii->i_block[12]);
                blkid = e2ii->i_block[12];
                blk_slot = ext2_find_inotable_slot(inode, blkid, rel_inoblk, 1);
        } else {
                /* Direct block, straight out of the inode */
                blk_slot = &e2ii->i_block[ino_block];
                /* need to incref, since the i_block isn't a real metablock (it's just a
                 * random page!), and the caller is going to end up decreffing it */
                page_incref(kva2page(blk_slot));
        }
        return blk_slot;
}

/* Determines the FS block id for a given inode block id.  Convenience wrapper
 * that may go away soon. */
uint32_t ext2_find_inoblock(struct inode *inode, unsigned int ino_block)
{
        uint32_t retval, *buf = ext2_lookup_inotable_slot(inode, ino_block);
        retval = *buf;
        ext2_put_metablock(buf);
        return retval;
}

/* Returns a kmalloc'd block for the contents of the ino block.  Kept around for
 * a couple commits, will prob go away soon */
void *ext2_read_ino_block(struct inode *inode, unsigned int ino_block)
{
        unsigned long blkid = ext2_find_inoblock(inode, ino_block);
        return ext2_read_fileblock(inode->i_sb, blkid);
}

/* This should help with degubbing.  In read_inode(), print out the i_block, and
 * consider manually (via memory inspection) examining those blocks.  Odds are,
 * the 2x and 3x walks are jacked up. */
void ext2_print_ino_blocks(struct inode *inode)
{
        printk("Inode %08p, Size: %d, 512B 'blocks;: %d\n-------------\n", inode,
               inode->i_size, inode->i_blocks);
        for (int i = 0; i < inode->i_blocks; i++)
                printk("# %03d, Block %03d\n", i, ext2_find_inoblock(inode, i));
}

/* Misc Functions */

/* This checks an ext2 disc SB for consistency, optionally printing out its
 * stats.  It also will also read in a copy of the block group descriptor table
 * from its first location (right after the primary SB copy) */
void ext2_check_sb(struct ext2_sb *e2sb, struct ext2_block_group *bg,
                   bool print)
{
        int retval;
        unsigned int blksize, blks_per_group, num_blk_group, num_blks;
        unsigned int inodes_per_grp, inode_size;
        unsigned int sum_blks = 0, sum_inodes = 0;

        assert(le16_to_cpu(e2sb->s_magic) == EXT2_SUPER_MAGIC);
        num_blks = le32_to_cpu(e2sb->s_blocks_cnt);
        blksize = 1024 << le32_to_cpu(e2sb->s_log_block_size);
        blks_per_group = le32_to_cpu(e2sb->s_blocks_per_group);
        num_blk_group = num_blks / blks_per_group + (num_blks % blks_per_group ? 1 : 0);
        
        if (print) {
                printk("EXT2 info:\n-------------------------\n");
                printk("Total Inodes:     %8d\n", le32_to_cpu(e2sb->s_inodes_cnt));
                printk("Total Blocks:     %8d\n", le32_to_cpu(e2sb->s_blocks_cnt));
                printk("Num R-Blocks:     %8d\n", le32_to_cpu(e2sb->s_rblocks_cnt));
                printk("Num Free Blocks:  %8d\n", le32_to_cpu(e2sb->s_free_blocks_cnt));
                printk("Num Free Inodes:  %8d\n", le32_to_cpu(e2sb->s_free_inodes_cnt));
                printk("First Data Block: %8d\n",
                       le32_to_cpu(e2sb->s_first_data_block));
                printk("Block Size:       %8d\n",
                       1024 << le32_to_cpu(e2sb->s_log_block_size));
                printk("Fragment Size:    %8d\n",
                       1024 << le32_to_cpu(e2sb->s_log_frag_size));
                printk("Blocks per group: %8d\n",
                       le32_to_cpu(e2sb->s_blocks_per_group));
                printk("Inodes per group: %8d\n",
                       le32_to_cpu(e2sb->s_inodes_per_group));
                printk("Block groups:     %8d\n", num_blk_group);
                printk("Mount state:      %8d\n", le16_to_cpu(e2sb->s_state));
                printk("Rev Level:        %8d\n", le32_to_cpu(e2sb->s_minor_rev_level));
                printk("Minor Rev Level:  %8d\n", le16_to_cpu(e2sb->s_minor_rev_level));
                printk("Creator OS:       %8d\n", le32_to_cpu(e2sb->s_creator_os));
                printk("First Inode:      %8d\n", le32_to_cpu(e2sb->s_first_ino));
                printk("Inode size:       %8d\n", le16_to_cpu(e2sb->s_inode_size));
                printk("This block group: %8d\n", le16_to_cpu(e2sb->s_block_group_nr));
                printk("BG ID of 1st meta:%8d\n", le16_to_cpu(e2sb->s_first_meta_bg));
                printk("Volume name:      %s\n", e2sb->s_volume_name);
                printk("\nBlock Group Info:\n----------------------\n");
        }
        
        for (int i = 0; i < num_blk_group; i++) {
                sum_blks += le16_to_cpu(bg[i].bg_free_blocks_cnt);
                sum_inodes += le16_to_cpu(bg[i].bg_free_inodes_cnt);
                if (print) {
                        printk("*** BG %d at %08p\n", i, &bg[i]);
                        printk("Block bitmap:%8d\n", le32_to_cpu(bg[i].bg_block_bitmap));
                        printk("Inode bitmap:%8d\n", le32_to_cpu(bg[i].bg_inode_bitmap));
                        printk("Inode table: %8d\n", le32_to_cpu(bg[i].bg_inode_table));
                        printk("Free blocks: %8d\n", le16_to_cpu(bg[i].bg_free_blocks_cnt));
                        printk("Free inodes: %8d\n", le16_to_cpu(bg[i].bg_free_inodes_cnt));
                        printk("Used Dirs:   %8d\n", le16_to_cpu(bg[i].bg_used_dirs_cnt));
                }
        }
        
        /* Sanity Assertions.  A good ext2 will always pass these. */
        inodes_per_grp = le32_to_cpu(e2sb->s_inodes_per_group);
        blks_per_group = le32_to_cpu(e2sb->s_blocks_per_group);
        inode_size = le32_to_cpu(e2sb->s_inode_size);
        assert(le32_to_cpu(e2sb->s_inodes_cnt) <= inodes_per_grp * num_blk_group);
        assert(le32_to_cpu(e2sb->s_free_inodes_cnt) == sum_inodes);
        assert(le32_to_cpu(e2sb->s_blocks_cnt) <= blks_per_group * num_blk_group);
        assert(le32_to_cpu(e2sb->s_free_blocks_cnt) == sum_blks);
        if (blksize == 1024)
                assert(le32_to_cpu(e2sb->s_first_data_block) == 1);
        else
                assert(le32_to_cpu(e2sb->s_first_data_block) == 0);
        assert(inode_size <= blksize);
        assert(inode_size == 1 << LOG2_UP(inode_size));
        assert(blksize * 8 >= inodes_per_grp);
        assert(inodes_per_grp % (blksize / inode_size) == 0);
        if (print)
                printk("Passed EXT2 Checks\n");
}

/* VFS required Misc Functions */

/* Creates the SB.  Like with Ext2's, we should consider pulling out the
 * FS-independent stuff, if possible. */
struct super_block *ext2_get_sb(struct fs_type *fs, int flags,
                               char *dev_name, struct vfsmount *vmnt)
{
        struct block_device *bdev;
        struct ext2_sb *e2sb;
        struct ext2_block_group *e2bg;
        unsigned int blks_per_group, num_blk_group, num_blks;

        static bool ran_once = FALSE;
        if (!ran_once) {
                ran_once = TRUE;
                ext2_init();
        }
        bdev = get_bdev(dev_name);
        assert(bdev);
        /* Read the SB.  It's always at byte 1024 and 1024 bytes long.  Note we do
         * not put the metablock (we pin it off the sb later).  Same with e2bg. */
        e2sb = (struct ext2_sb*)__ext2_get_metablock(bdev, 1, 1024);
        if (!(le16_to_cpu(e2sb->s_magic) == EXT2_SUPER_MAGIC)) {
                warn("EXT2 Not detected when it was expected!");
                return 0;
        }
        /* Read in the block group descriptor table.  Which block the BG table is on
         * depends on the blocksize */
        unsigned int blksize = 1024 << le32_to_cpu(e2sb->s_log_block_size);
        e2bg = __ext2_get_metablock(bdev, blksize == 1024 ? 2 : 1, blksize);
        assert(e2bg);
        ext2_check_sb(e2sb, e2bg, FALSE);

        /* Now we build and init the VFS SB */
        struct super_block *sb = get_sb();
        sb->s_dev = 0;                  /* what do we really want here? */
        sb->s_blocksize = blksize;
        /* max file size for a 1024 blocksize FS.  good enough for now (TODO) */
        sb->s_maxbytes = 17247252480;
        sb->s_type = &ext2_fs_type;
        sb->s_op = &ext2_s_op;
        sb->s_flags = flags;    /* from the disc too?  which flags are these? */
        sb->s_magic = EXT2_SUPER_MAGIC;
        sb->s_mount = vmnt;     /* Kref?  also in KFS */
        sb->s_syncing = FALSE;
        kref_get(&bdev->b_kref, 1);
        sb->s_bdev = bdev;
        strlcpy(sb->s_name, "EXT2", 32);
        sb->s_fs_info = kmalloc(sizeof(struct ext2_sb_info), 0);
        assert(sb->s_fs_info);
        /* store the in-memory copy of the disk SB and bg desc table */
        ((struct ext2_sb_info*)sb->s_fs_info)->e2sb = e2sb;
        ((struct ext2_sb_info*)sb->s_fs_info)->e2bg = e2bg;
        /* Precompute the number of BGs */
        num_blks = le32_to_cpu(e2sb->s_blocks_cnt);
        blks_per_group = le32_to_cpu(e2sb->s_blocks_per_group);
        ((struct ext2_sb_info*)sb->s_fs_info)->nr_bgs = num_blks / blks_per_group +
                                               (num_blks % blks_per_group ? 1 : 0);

        /* Final stages of initializing the sb, mostly FS-independent */
        init_sb(sb, vmnt, &ext2_d_op, EXT2_ROOT_INO, 0);

        printk("EXT2 superblock loaded\n");
        kref_put(&bdev->b_kref);
        return sb;
}

void ext2_kill_sb(struct super_block *sb)
{
        /* don't forget to kfree the s_fs_info and its two members */
        panic("Killing an EXT2 SB is not supported!");
}

/* Every FS must have a static FS Type, with which the VFS code can bootstrap */
struct fs_type ext2_fs_type = {"EXT2", 0, ext2_get_sb, ext2_kill_sb, {0, 0},
                               TAILQ_HEAD_INITIALIZER(ext2_fs_type.fs_supers)};

/* Page Map Operations */

/* Sets up the bidirectional mapping between the page and its buffer heads.  As
 * a future optimization, we could try and detect if all of the blocks are
 * contiguous (either before or after making them) and compact them to one BH.
 * Note there is an assumption that the file has at least one block in it. */
int ext2_mappage(struct page_map *pm, struct page *page)
{
        struct buffer_head *bh;
        struct inode *inode = (struct inode*)pm->pm_host;
        assert(!page->pg_private);              /* double check that we aren't bh-mapped */
        assert(inode->i_mapping == pm); /* double check we are the inode for pm */
        struct block_device *bdev = inode->i_sb->s_bdev;
        unsigned int blk_per_pg = PGSIZE / inode->i_sb->s_blocksize;
        unsigned int sct_per_blk = inode->i_sb->s_blocksize / bdev->b_sector_sz;
        uint32_t ino_blk_num, fs_blk_num = 0, *fs_blk_slot;

        bh = kmem_cache_alloc(bh_kcache, 0);
        page->pg_private = bh;
        for (int i = 0; i < blk_per_pg; i++) {
                /* free_bh() can handle having a halfway aborted mappage() */
                if (!bh)
                        return -ENOMEM;
                bh->bh_page = page;                                                     /* weak ref */
                bh->bh_buffer = page2kva(page) + i * inode->i_sb->s_blocksize;
                bh->bh_flags = 0;                                                       /* whatever... */
                bh->bh_bdev = bdev;                                                     /* uncounted ref */
                /* compute the first sector of the FS block for the ith buf in the pg */
                ino_blk_num = page->pg_index * blk_per_pg + i;
                fs_blk_slot = ext2_lookup_inotable_slot(inode, ino_blk_num);
                /* If there isn't a block there, lets get one.  The previous fs_blk_num
                 * is our hint (or we have to compute one). */
                if (!*fs_blk_slot) {
                        if (!fs_blk_num) {
                                fs_blk_num = ext2_bgidx2block(inode->i_sb,
                                                              ext2_inode2bg(inode), 0);
                        }
                        fs_blk_num = ext2_alloc_block(inode, fs_blk_num + 1);
                        /* Link it, and dirty the inode indirect block */
                        *fs_blk_slot = cpu_to_le32(fs_blk_num);
                        ext2_dirty_metablock(fs_blk_slot);
                        /* the block is still on disk, and we don't want its contents */
                        bh->bh_flags = BH_NEEDS_ZEROED;                 /* talking to readpage */
                        /* update our num blocks, with 512B each "block" (ext2-style) */
                        inode->i_blocks += inode->i_sb->s_blocksize >> 9;
                } else {        /* there is a block there already */
                        fs_blk_num = *fs_blk_slot;
                }
                ext2_put_metablock(fs_blk_slot);
                bh->bh_sector = fs_blk_num * sct_per_blk;
                bh->bh_nr_sector = sct_per_blk;
                /* Stop if we're the last block in the page.  We could be going beyond
                 * the end of the file, in which case the next BHs will be zeroed. */
                if (i == blk_per_pg - 1) {
                        bh->bh_next = 0;
                        break;
                } else {
                        /* get and link to the next BH. */
                        bh->bh_next = kmem_cache_alloc(bh_kcache, 0);
                        bh = bh->bh_next;
                }
        }
        return 0;
}

/* Fills page with its contents from its backing store file.  Note that we do
 * the zero padding here, instead of higher in the VFS.  Might change in the
 * future.  TODO: make this a block FS generic call. */
int ext2_readpage(struct page_map *pm, struct page *page)
{
        int retval;
        struct block_device *bdev = pm->pm_host->i_sb->s_bdev;
        struct buffer_head *bh;
        struct block_request *breq;
        void *eobh;

        assert(page->pg_flags & PG_BUFFER);
        retval = ext2_mappage(pm, page);
        if (retval) {
                unlock_page(page);
                return retval;
        }
        /* Build and submit the request */
        breq = kmem_cache_alloc(breq_kcache, 0);
        if (!breq) {
                unlock_page(page);
                return -ENOMEM;
        }
        breq->flags = BREQ_READ;
        breq->bhs = breq->local_bhs;
        breq->nr_bhs = 0;
        /* Pack the BH pointers in the block request */
        bh = (struct buffer_head*)page->pg_private;
        assert(bh);
        /* Either read the block in, or zero the buffer.  If we wanted to ensure no
         * data is leaked after a crash, we'd write a 0 block too. */
        for (int i = 0; bh; bh = bh->bh_next) {
                if (!(bh->bh_flags & BH_NEEDS_ZEROED)) {
                        breq->bhs[i] = bh;
                        breq->nr_bhs++;
                        i++;
                } else {
                        memset(bh->bh_buffer, 0, pm->pm_host->i_sb->s_blocksize);
                        bh->bh_flags |= BH_DIRTY;
                        bh->bh_page->pg_flags |= PG_DIRTY;
                }
        }
        /* TODO: (BLK) this assumes we slept til the request was done */
        retval = make_request(bdev, breq);
        assert(!retval);
        /* zero out whatever is beyond the EOF.  we could do this by figuring out
         * where the BHs end and zeroing from there, but I'd rather zero from where
         * the file ends (which could be in the middle of an FS block */
        uintptr_t eof_off;
        eof_off = (pm->pm_host->i_size - page->pg_index * PGSIZE);
        eof_off = MIN(eof_off, PGSIZE) % PGSIZE;
        /* at this point, eof_off is the offset into the page of the EOF, or 0 */
        if (eof_off)
                memset(eof_off + page2kva(page), 0, PGSIZE - eof_off);
        /* after the data is read, we mark it up to date and unlock the page. */
        page->pg_flags |= PG_UPTODATE;
        unlock_page(page);
        kmem_cache_free(breq_kcache, breq);
        /* Useful debugging.  Put one higher up if the page is not getting mapped */
        //print_pageinfo(page);
        return 0;
}

/* Super Operations */

/* Creates and initializes a new inode.  FS specific, yet inode-generic fields
 * are filled in.  inode-specific fields are filled in in read_inode() based on
 * what's on the disk for a given i_no.  i_no and i_fop are set by the caller.
 *
 * Note that this means this inode can be for an inode that is already on disk,
 * or it can be used when creating.  The i_fop depends on the type of file
 * (file, directory, symlink, etc). */
struct inode *ext2_alloc_inode(struct super_block *sb)
{
        struct inode *inode = kmem_cache_alloc(inode_kcache, 0);
        memset(inode, 0, sizeof(struct inode));
        inode->i_op = &ext2_i_op;
        inode->i_pm.pm_op = &ext2_pm_op;
        return inode;
}

/* FS-specific clean up when an inode is dealloced.  this is just cleaning up
 * the in-memory version, and only the FS-specific parts.  whether or not the
 * inode is still on disc is irrelevant. */
void ext2_dealloc_inode(struct inode *inode)
{
        kmem_cache_free(ext2_i_kcache, inode->i_fs_info);
}

/* reads the inode data on disk specified by inode->i_ino into the inode.
 * basically, it's a "make this inode the one for i_ino (i number)" */
void ext2_read_inode(struct inode *inode)
{
        unsigned int bg_idx, ino_per_blk, my_ino_blk;
        struct ext2_sb_info *e2sbi = (struct ext2_sb_info*)inode->i_sb->s_fs_info;
        struct ext2_block_group *my_bg;
        struct ext2_inode *ino_tbl_chunk, *my_ino;

        /* Need to compute the blockgroup and index of the requested inode */
        ino_per_blk = inode->i_sb->s_blocksize /
                      le16_to_cpu(e2sbi->e2sb->s_inode_size);
        bg_idx = ext2_inode2bgidx(inode);
        my_bg = ext2_inode2bg(inode);
        /* Figure out which FS block of the inode table we want and read in that
         * chunk */
        my_ino_blk = le32_to_cpu(my_bg->bg_inode_table) + bg_idx / ino_per_blk;
        ino_tbl_chunk = ext2_get_metablock(inode->i_sb, my_ino_blk);
        my_ino = &ino_tbl_chunk[bg_idx % ino_per_blk];

        /* Have the disk inode now, let's put its info into the VFS inode: */
        inode->i_mode = le16_to_cpu(my_ino->i_mode);
        switch (inode->i_mode & __S_IFMT) {
                case (__S_IFDIR):
                        inode->i_fop = &ext2_f_op_dir;
                        break;
                case (__S_IFREG):
                        inode->i_fop = &ext2_f_op_file;
                        break;
                case (__S_IFLNK):
                        inode->i_fop = &ext2_f_op_sym;
                        break;
                case (__S_IFCHR):
                case (__S_IFBLK):
                default:
                        inode->i_fop = &ext2_f_op_file;
                        warn("[Calm British Accent] Look around you.  Unhandled filetype.");
        }
        inode->i_nlink = le16_to_cpu(my_ino->i_links_cnt);
        inode->i_uid = le16_to_cpu(my_ino->i_uid);
        inode->i_gid = le16_to_cpu(my_ino->i_gid);
        /* technically, for large F_REG, we should | with i_dir_acl */
        inode->i_size = le32_to_cpu(my_ino->i_size);
        inode->i_atime.tv_sec = le32_to_cpu(my_ino->i_atime);
        inode->i_atime.tv_nsec = 0;
        inode->i_mtime.tv_sec = le32_to_cpu(my_ino->i_mtime);
        inode->i_mtime.tv_nsec = 0;
        inode->i_ctime.tv_sec = le32_to_cpu(my_ino->i_ctime);
        inode->i_ctime.tv_nsec = 0;
        inode->i_blocks = le32_to_cpu(my_ino->i_blocks);
        inode->i_flags = le32_to_cpu(my_ino->i_flags);
        inode->i_socket = FALSE;                /* for now */
        /* Copy over the other inode stuff that isn't in the VFS inode.  For now,
         * it's just the block pointers */
        inode->i_fs_info = kmem_cache_alloc(ext2_i_kcache, 0);
        struct ext2_i_info *e2ii = (struct ext2_i_info*)inode->i_fs_info;
        for (int i = 0; i < 15; i++)
                e2ii->i_block[i] = le32_to_cpu(my_ino->i_block[i]);
        /* TODO: (HASH) unused: inode->i_hash add to hash (saves on disc reading) */
        /* TODO: we could consider saving a pointer to the disk inode and pinning
         * its buffer in memory, but for now we'll just free it. */
        ext2_put_metablock(ino_tbl_chunk);
}

/* called when an inode in memory is modified (journalling FS's care) */
void ext2_dirty_inode(struct inode *inode)
{
        // presumably we'll ext2_dirty_metablock(void *buffer) here
}

/* write the inode to disk (specifically, to inode inode->i_ino), synchronously
 * if we're asked to wait */
void ext2_write_inode(struct inode *inode, bool wait)
{
I_AM_HERE;
}

/* called when an inode is decref'd, to do any FS specific work */
void ext2_put_inode(struct inode *inode)
{
I_AM_HERE;
}

/* Unused for now, will get rid of this if inode_release is sufficient */
void ext2_drop_inode(struct inode *inode)
{
I_AM_HERE;
}

/* delete the inode from disk (all data) */
void ext2_delete_inode(struct inode *inode)
{
I_AM_HERE;
        // would remove from "disk" here
        /* TODO: give up our i_ino */
}

/* unmount and release the super block */
void ext2_put_super(struct super_block *sb)
{
        panic("Shazbot! Ext2 can't be unmounted yet!");
}

/* updates the on-disk SB with the in-memory SB */
void ext2_write_super(struct super_block *sb)
{
I_AM_HERE;
}

/* syncs FS metadata with the disc, synchronously if we're waiting.  this info
 * also includes anything pointed to by s_fs_info. */
int ext2_sync_fs(struct super_block *sb, bool wait)
{
I_AM_HERE;
        return 0;
}

/* remount the FS with the new flags */
int ext2_remount_fs(struct super_block *sb, int flags, char *data)
{
        warn("Ext2 will not remount.");
        return -1; // can't remount
}

/* interrupts a mount operation - used by NFS and friends */
void ext2_umount_begin(struct super_block *sb)
{
        panic("Cannot abort a Ext2 mount, and why would you?");
}

/* inode_operations */

/* Little helper, used for initializing new inodes for file-like objects (files,
 * symlinks, etc).  We pass the dentry, since we need to up it. */
static void ext2_init_inode(struct inode *dir, struct dentry *dentry)
{
#if 0
        struct inode *inode = dentry->d_inode;
        inode->i_ino = ext2_get_free_ino();
#endif
}

/* Called when creating a new disk inode in dir associated with dentry.  We need
 * to fill out the i_ino, set the type, and do whatever else we need */
int ext2_create(struct inode *dir, struct dentry *dentry, int mode,
               struct nameidata *nd)
{
I_AM_HERE;
        #if 0
        struct inode *inode = dentry->d_inode;
        ext2_init_inode(dir, dentry);
        SET_FTYPE(inode->i_mode, __S_IFREG);
        inode->i_fop = &ext2_f_op_file;
        /* fs_info->filestart is set by the caller, or else when first written (for
         * new files.  it was set to 0 in alloc_inode(). */
        #endif
        return 0;
}

/* Searches the directory for the filename in the dentry, filling in the dentry
 * with the FS specific info of this file.  If it succeeds, it will pass back
 * the *dentry you should use (which might be the same as the one you passed in).
 * If this fails, it will return 0, but not free the memory of "dentry."
 *
 * Callers, make sure you alloc and fill out the name parts of the dentry.  We
 * don't currently use the ND.  Might remove it in the future.  */
struct dentry *ext2_lookup(struct inode *dir, struct dentry *dentry,
                           struct nameidata *nd)
{
        assert(S_ISDIR(dir->i_mode));
        struct ext2_dirent *dir_buf, *dir_i;
        unsigned int dir_block = 0;
        bool found = FALSE;
        dir_buf = ext2_read_ino_block(dir, dir_block++);
        dir_i = dir_buf;
        /* now we have the first block worth of dirents.  We'll get another block if
         * dir_i hits a block boundary */
        for (unsigned int bytes = 0; bytes < dir->i_size; ) {
                /* On subsequent loops, we might need to advance to the next block */
                if ((void*)dir_i >= (void*)dir_buf + dir->i_sb->s_blocksize) {
                        kfree(dir_buf);
                        dir_buf = ext2_read_ino_block(dir, dir_block++);
                        dir_i = dir_buf;
                        assert(dir_buf);
                }
                /* Test if we're the one (TODO: use d_compare) */
                if (!strncmp((char*)dir_i->dir_name, dentry->d_name.name,
                             dir_i->dir_namelen)){
                        load_inode(dentry, le32_to_cpu(dir_i->dir_inode));
                        /* TODO: (HASH) add dentry to dcache (maybe the caller should) */
                        kfree(dir_buf);
                        return dentry;
                }
                /* Get ready for the next loop */
                bytes += dir_i->dir_reclen;
                dir_i = (void*)dir_i + dir_i->dir_reclen;
        }
        printd("EXT2: Not Found, %s\n", dentry->d_name.name);   
        kfree(dir_buf);
        return 0;
}

/* Hard link to old_dentry in directory dir with a name specified by new_dentry.
 * At the very least, set the new_dentry's FS-specific fields. */
int ext2_link(struct dentry *old_dentry, struct inode *dir,
             struct dentry *new_dentry)
{
I_AM_HERE;
        assert(new_dentry->d_op = &ext2_d_op);
        return 0;
}

/* Removes the link from the dentry in the directory */
int ext2_unlink(struct inode *dir, struct dentry *dentry)
{
I_AM_HERE;
        return 0;
}

/* Creates a new inode for a symlink dir, linking to / containing the name
 * symname.  dentry is the controlling dentry of the inode. */
int ext2_symlink(struct inode *dir, struct dentry *dentry, const char *symname)
{
I_AM_HERE;
        #if 0
        struct inode *inode = dentry->d_inode;
        SET_FTYPE(inode->i_mode, __S_IFLNK);
        inode->i_fop = &ext2_f_op_sym;
        strncpy(string, symname, len);
        string[len] = '\0';             /* symname should be \0d anyway, but just in case */
        #endif
        return 0;
}

/* Called when creating a new inode for a directory associated with dentry in
 * dir with the given mode.  Note, we might (later) need to track subdirs within
 * the parent inode, like we do with regular files.  I'd rather not, so we'll
 * see if we need it. */
int ext2_mkdir(struct inode *dir, struct dentry *dentry, int mode)
{
I_AM_HERE;
        #if 0
        struct inode *inode = dentry->d_inode;
        inode->i_ino = ext2_get_free_ino();
        SET_FTYPE(inode->i_mode, __S_IFDIR);
        inode->i_fop = &ext2_f_op_dir;
        #endif
        return 0;
}

/* Removes from dir the directory 'dentry.'  Ext2 doesn't store anything in the
 * inode for which children it has.  It probably should, but since everything is
 * pinned, it just relies on the dentry connections. */
int ext2_rmdir(struct inode *dir, struct dentry *dentry)
{
I_AM_HERE;
        return 0;
}

/* Used to make a generic file, based on the type and the major/minor numbers
 * (in rdev), with the given mode.  As with others, this creates a new disk
 * inode for the file */
int ext2_mknod(struct inode *dir, struct dentry *dentry, int mode, dev_t rdev)
{
I_AM_HERE;
        return -1;
}

/* Moves old_dentry from old_dir to new_dentry in new_dir */
int ext2_rename(struct inode *old_dir, struct dentry *old_dentry,
               struct inode *new_dir, struct dentry *new_dentry)
{
I_AM_HERE;
        return -1;
}

/* Returns the char* for the symname for the given dentry.  The VFS code that
 * calls this for real FS's might assume it's already read in, so if the char *
 * isn't already in memory, we'd need to read it in here.  Regarding the char*
 * storage, the char* only will last as long as the dentry and inode are in
 * memory. */
char *ext2_readlink(struct dentry *dentry)
{
I_AM_HERE;
        struct inode *inode = dentry->d_inode;
        if (!S_ISLNK(inode->i_mode))
                return 0;
        return 0;
}

/* Modifies the size of the file of inode to whatever its i_size is set to */
void ext2_truncate(struct inode *inode)
{
}

/* Checks whether the the access mode is allowed for the file belonging to the
 * inode.  Implies that the permissions are on the file, and not the hardlink */
int ext2_permission(struct inode *inode, int mode, struct nameidata *nd)
{
        return -1;
}


/* dentry_operations */
/* Determines if the dentry is still valid before using it to translate a path.
 * Network FS's need to deal with this. */
int ext2_d_revalidate(struct dentry *dir, struct nameidata *nd)
{ // default, nothing
        return -1;
}

/* Produces the hash to lookup this dentry from the dcache */
int ext2_d_hash(struct dentry *dentry, struct qstr *name)
{
        return -1;
}

/* Compares name1 and name2.  name1 should be a member of dir. */
int ext2_d_compare(struct dentry *dir, struct qstr *name1, struct qstr *name2)
{ // default, string comp (case sensitive)
        return -1;
}

/* Called when the last ref is deleted (refcnt == 0) */
int ext2_d_delete(struct dentry *dentry)
{ // default, nothin
        return -1;
}

/* Called when it's about to be slab-freed */
int ext2_d_release(struct dentry *dentry)
{
        return -1;
}

/* Called when the dentry loses it's inode (becomes "negative") */
void ext2_d_iput(struct dentry *dentry, struct inode *inode)
{ // default, call i_put to release the inode object
}


/* file_operations */

/* Updates the file pointer.  TODO: think about locking, and putting this in the
 * VFS. */
#include <syscall.h>    /* just for set_errno, may go away later */
off_t ext2_llseek(struct file *file, off_t offset, int whence)
{
        off_t temp_off = 0;
        switch (whence) {
                case SEEK_SET:
                        temp_off = offset;
                        break;
                case SEEK_CUR:
                        temp_off = file->f_pos + offset;
                        break;
                case SEEK_END:
                        temp_off = file->f_dentry->d_inode->i_size + offset;
                        break;
                default:
                        set_errno(EINVAL);
                        warn("Unknown 'whence' in llseek()!\n");
                        return -1;
        }
        file->f_pos = temp_off;
        return temp_off;
}

/* Fills in the next directory entry (dirent), starting with d_off.  Like with
 * read and write, there will be issues with userspace and the *dirent buf.
 * TODO: (UMEM) */
int ext2_readdir(struct file *dir, struct dirent *dirent)
{
        void *buffer;
        /* Not enough data at the end of the directory */
        if (dir->f_dentry->d_inode->i_size <
            dirent->d_off + sizeof(struct ext2_dirent))
                return -ENOENT;
        
        /* Figure out which block we need to read in for dirent->d_off */
        int block = dirent->d_off / dir->f_dentry->d_sb->s_blocksize;
        buffer = ext2_read_ino_block(dir->f_dentry->d_inode, block);
        assert(buffer);
        off_t f_off = dirent->d_off % dir->f_dentry->d_sb->s_blocksize;
        /* Copy out the dirent info */
        struct ext2_dirent *e2dir = (struct ext2_dirent*)(buffer + f_off);
        dirent->d_ino = le32_to_cpu(e2dir->dir_inode);
        dirent->d_off += le16_to_cpu(e2dir->dir_reclen);
        /* note, dir_namelen doesn't include the \0 */
        dirent->d_reclen = e2dir->dir_namelen;
        strncpy(dirent->d_name, (char*)e2dir->dir_name, e2dir->dir_namelen);
        assert(e2dir->dir_namelen <= MAX_FILENAME_SZ);
        dirent->d_name[e2dir->dir_namelen] = '\0';
        kfree(buffer);
        
        /* At the end of the directory, sort of.  ext2 often preallocates blocks, so
         * this will cause us to walk along til the end, which isn't quite right. */
        if (dir->f_dentry->d_inode->i_size == dirent->d_off)
                return 0;
        if (dir->f_dentry->d_inode->i_size < dirent->d_off) {
                warn("Issues reaching the end of an ext2 directory!");
                return 0;
        }
        return 1;                                                       /* normal success for readdir */
}

/* This is called when a VMR is mapping a particular file.  The FS needs to do
 * whatever it needs so that faults can be handled by read_page(), and handle all
 * of the cases of MAP_SHARED, MAP_PRIVATE, whatever.  It also needs to ensure
 * the file is not being mmaped in a way that conflicts with the manner in which
 * the file was opened or the file type. */
int ext2_mmap(struct file *file, struct vm_region *vmr)
{
        if (S_ISREG(file->f_dentry->d_inode->i_mode))
                return 0;
        return -1;
}

/* Called by the VFS while opening the file, which corresponds to inode,  for
 * the FS to do whatever it needs. */
int ext2_open(struct inode *inode, struct file *file)
{
        /* TODO: check to make sure the file is openable, and maybe do some checks
         * for the open mode (like did we want to truncate, append, etc) */
        return 0;
}

/* Called when a file descriptor is closed. */
int ext2_flush(struct file *file)
{
I_AM_HERE;
        return -1;
}

/* Called when the file is about to be closed (file obj freed) */
int ext2_release(struct inode *inode, struct file *file)
{
        return 0;
}

/* Flushes the file's dirty contents to disc */
int ext2_fsync(struct file *file, struct dentry *dentry, int datasync)
{
        return -1;
}

/* Traditionally, sleeps until there is file activity.  We probably won't
 * support this, or we'll handle it differently. */
unsigned int ext2_poll(struct file *file, struct poll_table_struct *poll_table)
{
        return -1;
}

/* Reads count bytes from a file, starting from (and modifiying) offset, and
 * putting the bytes into buffers described by vector */
ssize_t ext2_readv(struct file *file, const struct iovec *vector,
                  unsigned long count, off_t *offset)
{
        return -1;
}

/* Writes count bytes to a file, starting from (and modifiying) offset, and
 * taking the bytes from buffers described by vector */
ssize_t ext2_writev(struct file *file, const struct iovec *vector,
                  unsigned long count, off_t *offset)
{
        return -1;
}

/* Write the contents of file to the page.  Will sort the params later */
ssize_t ext2_sendpage(struct file *file, struct page *page, int offset,
                     size_t size, off_t pos, int more)
{
        return -1;
}

/* Checks random FS flags.  Used by NFS. */
int ext2_check_flags(int flags)
{ // default, nothing
        return -1;
}

/* Redeclaration and initialization of the FS ops structures */
struct page_map_operations ext2_pm_op = {
        ext2_readpage,
};

struct super_operations ext2_s_op = {
        ext2_alloc_inode,
        ext2_dealloc_inode,
        ext2_read_inode,
        ext2_dirty_inode,
        ext2_write_inode,
        ext2_put_inode,
        ext2_drop_inode,
        ext2_delete_inode,
        ext2_put_super,
        ext2_write_super,
        ext2_sync_fs,
        ext2_remount_fs,
        ext2_umount_begin,
};

struct inode_operations ext2_i_op = {
        ext2_create,
        ext2_lookup,
        ext2_link,
        ext2_unlink,
        ext2_symlink,
        ext2_mkdir,
        ext2_rmdir,
        ext2_mknod,
        ext2_rename,
        ext2_readlink,
        ext2_truncate,
        ext2_permission,
};

struct dentry_operations ext2_d_op = {
        ext2_d_revalidate,
        ext2_d_hash,
        ext2_d_compare,
        ext2_d_delete,
        ext2_d_release,
        ext2_d_iput,
};

struct file_operations ext2_f_op_file = {
        ext2_llseek,
        generic_file_read,
        generic_file_write,
        ext2_readdir,
        ext2_mmap,
        ext2_open,
        ext2_flush,
        ext2_release,
        ext2_fsync,
        ext2_poll,
        ext2_readv,
        ext2_writev,
        ext2_sendpage,
        ext2_check_flags,
};

struct file_operations ext2_f_op_dir = {
        ext2_llseek,
        generic_dir_read,
        0,
        ext2_readdir,
        ext2_mmap,
        ext2_open,
        ext2_flush,
        ext2_release,
        ext2_fsync,
        ext2_poll,
        ext2_readv,
        ext2_writev,
        ext2_sendpage,
        ext2_check_flags,
};

struct file_operations ext2_f_op_sym = {
        ext2_llseek,
        generic_file_read,
        generic_file_write,
        ext2_readdir,
        ext2_mmap,
        ext2_open,
        ext2_flush,
        ext2_release,
        ext2_fsync,
        ext2_poll,
        ext2_readv,
        ext2_writev,
        ext2_sendpage,
        ext2_check_flags,
};