Re: [Ext4 punch hole 4/5] Ext4 Punch Hole Support: Enable Punch Hole

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On Tue, Mar 1, 2011 at 5:09 AM, Allison Henderson
<achender@xxxxxxxxxxxxxxxxxx> wrote:
> This patch adds the  new "ext4_punch_hole" "ext4_ext_punch_hole" routines.
>
> fallocate has been modified to call ext4_punch_hole when the punch hole
> flag is passed.  At the moment, we only support punching holes in
> extents, so this routine is pretty much a wrapper for the ext4_ext_punch_hole
> routine.
>
> The ext4_ext_punch_hole routine zeros out the pages that are
> covered by the hole.  The blocks to be punched out
> are then identified as mapped, delayed, or already punched out.
> The blocks that mapped are the converted to into uninitialized
> extents.  The blocks are then punched out using the
> "ext4_ext_release_blocks" routine.
>
> Some minor utility functions have also been added.
> A new ext4_ext_lookup_hole routine is used by
> ext4_ext_punch_hole to check if a range of blocks
> have already been punched out.
>
> A new ext4_ext_test_block_flag has also been
> added to identify the state of a block (ie mapped,
> delayed, ect)
>
> Signed-off-by: Allison Henderson <achender@xxxxxxxxxx>
> ---
> :100644 100644 43a5772... aeb86d6... M  fs/ext4/ext4.h
> :100644 100644 efbc3ef... 5713258... M  fs/ext4/extents.c
> :100644 100644 28c9137... 493c908... M  fs/ext4/inode.c
>  fs/ext4/ext4.h    |    2 +
>  fs/ext4/extents.c |  321 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
>  fs/ext4/inode.c   |   26 +++++
>  3 files changed, 345 insertions(+), 4 deletions(-)
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 43a5772..aeb86d6 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1729,6 +1729,7 @@ extern int ext4_change_inode_journal_flag(struct inode *, int);
>  extern int ext4_get_inode_loc(struct inode *, struct ext4_iloc *);
>  extern int ext4_can_truncate(struct inode *inode);
>  extern void ext4_truncate(struct inode *);
> +extern long  ext4_punch_hole(struct inode *inode,loff_t offset, loff_t length);
>  extern int ext4_truncate_restart_trans(handle_t *, struct inode *, int nblocks);
>  extern void ext4_set_inode_flags(struct inode *);
>  extern void ext4_get_inode_flags(struct ext4_inode_info *);
> @@ -2066,6 +2067,7 @@ extern int ext4_ext_index_trans_blocks(struct inode *inode, int nrblocks,
>  extern int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
>                               struct ext4_map_blocks *map, int flags);
>  extern void ext4_ext_truncate(struct inode *);
> +extern void ext4_ext_punch_hole(struct inode *inode, loff_t offset, loff_t length);
>  extern void ext4_ext_init(struct super_block *);
>  extern void ext4_ext_release(struct super_block *);
>  extern long ext4_fallocate(struct file *file, int mode, loff_t offset,
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index efbc3ef..5713258 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -2776,6 +2776,154 @@ out:
>  }
>
>  /*
> + * lookup_hole()
> + * Returns the numbers of consecutive blocks starting at "start"
> + * that are not contained within an extent
> + */
> +static int ext4_ext_lookup_hole(struct inode *inode, ext4_lblk_t start){
> +    struct super_block *sb = inode->i_sb;
> +       int depth = ext_depth(inode);
> +       struct ext4_ext_path *path;
> +       struct ext4_extent_header *eh;
> +       struct ext4_extent *ex;
> +       struct buffer_head *bh;
> +       ext4_lblk_t last_block;
> +       handle_t *handle;
> +       int i, err;
> +
> +       ext_debug("lookup hole since %u\n", start);
> +
> +       /* Make sure start is valid */
> +       last_block = inode->i_size >> EXT4_BLOCK_SIZE_BITS(sb);
> +       if(start >= last_block)
> +               return -EIO;
> +
> +       handle = ext4_journal_start(inode, depth + 1);
> +       if (IS_ERR(handle))
> +                       return PTR_ERR(handle);

This is strange. The name of the functions implies it is a readonly operation,
so why is a transaction needed?
You should probably document the reason for that and specify the changes
which this function may apply.

> +
> +       /*
> +        * We start scanning from right side, looking for
> +        * the left most block contained in the leaf, and
> +        * stopping when "start" is crossed.
> +        */
> +       depth = ext_depth(inode);
> +       path = kzalloc(sizeof(struct ext4_ext_path) * (depth + 1), GFP_NOFS);
> +       if (path == NULL) {
> +                       ext4_journal_stop(handle);
> +                       return -ENOMEM;
> +       }
> +       path[0].p_depth = depth;
> +       path[0].p_hdr = ext_inode_hdr(inode);
> +       if (ext4_ext_check(inode, path[0].p_hdr, depth)) {
> +               err = -EIO;
> +               goto out;
> +       }
> +       i = err = 0;
> +
> +       while (i >= 0 && err == 0) {
> +               if (i == depth) {
> +                       /* this is leaf block */
> +
> +                       eh = path[i].p_hdr;
> +                       if (eh != NULL){
> +                               if (eh->eh_entries == 0){
> +                                       err = -EIO;
> +                                       goto out;
> +                               }
> +
> +                               ex = EXT_LAST_EXTENT(eh);
> +                               while (ex != NULL && ex >= EXT_FIRST_EXTENT(eh)){
> +
> +                                       /*
> +                                        * If the entire extent apears before start
> +                                        * then we have passed the hole.
> +                                        */
> +                                       if(ex->ee_block + ex->ee_len <= start)
> +                                               goto out;
> +
> +                                       /*
> +                                        * If the start of the extent appears after
> +                                        * or on start, then mark this as the edge
> +                                        * of the hole
> +                                        */
> +                                       if(ex->ee_block >= start)
> +                                               last_block = ex->ee_block;
> +
> +                                       /*
> +                                        * If the extent contains start, then there
> +                                        * is no hole.
> +                                        */
> +                                       else if(ex->ee_block + ex->ee_len > start){
> +                                               last_block = start;
> +                                               goto out;
> +                                       }
> +
> +                                       ex--;
> +                               }
> +                       }
> +
> +                       /* root level has p_bh == NULL, brelse() eats this */
> +                       brelse(path[i].p_bh);
> +                       path[i].p_bh = NULL;
> +                       i--;
> +                       continue;
> +               }
> +
> +               /* this is index block */
> +               if (!path[i].p_hdr)
> +                       path[i].p_hdr = ext_block_hdr(path[i].p_bh);
> +
> +               if (!path[i].p_idx) {
> +                       /* this level hasn't been touched yet */
> +                       path[i].p_idx = EXT_LAST_INDEX(path[i].p_hdr);
> +                       path[i].p_block = le16_to_cpu(path[i].p_hdr->eh_entries)+1;
> +                       ext_debug("init index ptr: hdr 0x%p, num %d\n",
> +                       path[i].p_hdr,
> +                       le16_to_cpu(path[i].p_hdr->eh_entries));
> +               }
> +               else {
> +                       /* we were already here, see at next index */
> +                       path[i].p_idx--;
> +               }
> +
> +               ext_debug("level %d - index, first 0x%p, cur 0x%p\n",
> +               i, EXT_FIRST_INDEX(path[i].p_hdr),
> +               path[i].p_idx);
> +
> +               /* go to the next level */
> +               ext_debug("move to level %d (block %llu)\n",
> +                               i + 1, ext4_idx_pblock(path[i].p_idx));
> +               memset(path + i + 1, 0, sizeof(*path));
> +               bh = sb_bread(sb, ext4_idx_pblock(path[i].p_idx));
> +               if (!bh) {
> +                       err = -EIO;
> +                       break;
> +               }
> +               if (WARN_ON(i + 1 > depth)) {
> +                       err = -EIO;
> +                       break;
> +               }
> +               if (ext4_ext_check(inode, ext_block_hdr(bh), depth - i - 1)) {
> +                       err = -EIO;
> +                       break;
> +               }
> +
> +               path[i + 1].p_bh = bh;
> +
> +               i++;
> +
> +       }
> +out:
> +       ext4_ext_drop_refs(path);
> +       kfree(path);
> +       ext4_journal_stop(handle);
> +
> +       return err ? err : last_block - start;
> +
> +}
> +
> +/*
>  * called at mount time
>  */
>  void ext4_ext_init(struct super_block *sb)
> @@ -4029,6 +4177,172 @@ next:
>        return ret;
>  }
>
> +/*
> + * ext4_ext_test_block_flag
> + * Tests the buffer head associated with the given block
> + * to see if the state contains flag
> + *
> + * @inode:  The inode of the given file
> + * @block:  The block to test
> + * @flag:   The flag to check for
> + *
> + * Returns 0 on sucess or negative on err
> + */
> +static int ext4_ext_test_block_flag(struct inode *inode, ext4_lblk_t block, enum bh_state_bits flag){

(style) open { in new line.

> +       struct buffer_head *bh;
> +       struct page *page;
> +       struct address_space *mapping = inode->i_mapping;
> +       loff_t block_offset;
> +       int i, ret;
> +       unsigned long flag_mask = 1 << flag;
> +
> +       block_offset = block << EXT4_BLOCK_SIZE_BITS(inode->i_sb);
> +       page = find_or_create_page(mapping, block_offset >> PAGE_CACHE_SHIFT,
> +       mapping_gfp_mask(mapping) & ~__GFP_FS);
> +
> +       if (!page)
> +               return -EIO;
> +
> +       if (!page_has_buffers(page))
> +               create_empty_buffers(page, EXT4_BLOCK_SIZE(inode->i_sb), 0);
> +
> +       /* advance to the buffer that has the block offset  */
> +       bh = page_buffers(page);
> +       for (i = 0; i < block_offset; i+=EXT4_BLOCK_SIZE(inode->i_sb)) {
> +               bh = bh->b_this_page;
> +       }
> +
> +       if(bh->b_state & flag_mask)
> +               ret = 0;
> +       else
> +               ret = -1;
> +
> +       unlock_page(page);
> +       page_cache_release(page);
> +
> +       return ret;
> +
> +}
> +
> +/*
> + * ext4_ext_punch_hole
> + *
> + * Punches a hole of "length" bytes in a file starting
> + * at byte "offset"
> + *
> + * @inode:  The inode of the file to punch a hole in
> + * @offset: The starting byte offset of the hole
> + * @length: The length of the hole
> + *
> + */
> +void ext4_ext_punch_hole(struct inode *inode, loff_t offset, loff_t length)
> +{
> +       struct super_block *sb = inode->i_sb;
> +       ext4_lblk_t first_block, last_block, num_blocks, iblock = 0;
> +       struct address_space *mapping = inode->i_mapping;
> +       struct ext4_map_blocks map;
> +       handle_t *handle;
> +       loff_t first_block_offset, last_block_offset, block_len;
> +       int get_blocks_flags, err, ret = 0;
> +
> +       first_block = (offset + sb->s_blocksize - 1)
> +                       >> EXT4_BLOCK_SIZE_BITS(sb);
> +       last_block = (offset+length)  >> EXT4_BLOCK_SIZE_BITS(sb);
> +
> +       first_block_offset = first_block << EXT4_BLOCK_SIZE_BITS(sb);
> +       last_block_offset = last_block << EXT4_BLOCK_SIZE_BITS(sb);
> +
> +       err = ext4_writepage_trans_blocks(inode);

1. (style) err is not an appropriate name (even though is it
convenient to reuse it)
2. did you check if ext4_writepage_trans_blocks(inode) covers the credits
    needed for splitting 1 extent into 3? I suppose it does if it also
being used
    when converting a middle part of an uninitialized extent, but I
didn't check.

> +       handle = ext4_journal_start(inode, err);
> +       if (IS_ERR(handle))
> +               return;
> +
> +       /*
> +        * Now we need to zero out the un block aligned data.
> +        * If the file is smaller than a block, just
> +        * zero out the middle and return
> +        */
> +       if(first_block > last_block)
> +               ext4_block_zero_page_range(handle, mapping, offset, length);
> +       else{
> +               /* zero out the head of the hole before the first block */
> +               block_len  = first_block_offset - offset;
> +               if(block_len > 0)
> +                       ext4_block_zero_page_range(handle, mapping, offset, block_len);
> +
> +               /* zero out the tail of the hole after the last block */
> +               block_len = offset + length - last_block_offset;
> +               if(block_len > 0)
> +                       ext4_block_zero_page_range(handle, mapping,
> +                                       last_block_offset, block_len);
> +       }
> +
> +       /* If there are no blocks to remove, return now */
> +       if(first_block >= last_block){
> +               ext4_journal_stop(handle);
> +               return;
> +       }
> +
> +       /* Clear pages associated with the hole */
> +       if (mapping->nrpages)
> +               invalidate_inode_pages2_range(mapping, offset >> PAGE_CACHE_SHIFT,
> +                                               (offset+length) >> PAGE_CACHE_SHIFT );
> +
> +
> +       /* Loop over all the blocks and identify blocks that need to be punched out */
> +       iblock = first_block;
> +       while(iblock < last_block){
> +               map.m_lblk = iblock;
> +               map.m_len = last_block - iblock;
> +               ret = ext4_map_blocks(handle, inode, &map, 0);
> +
> +               /* If the blocks are mapped, release them */
> +               if(ret > 0){
> +                       num_blocks = ret;
> +                       ext4_ext_convert_blocks_uninit(inode, handle, iblock, num_blocks);
> +                       ext4_ext_release_blocks(inode, iblock, iblock+num_blocks);
> +                       goto next;
> +               }
> +
> +               /*
> +                * If they are not mapped
> +                * check to see if they are punched out
> +                */
> +               ret = ext4_ext_lookup_hole(inode, iblock);
> +               if(ret > 0){
> +                       num_blocks = ret;
> +                       goto next;
> +               }
> +
> +               /*
> +                * If the block could not be mapped, and
> +                * its not already punched out,
> +                * check to see if the block is delayed
> +                */
> +               if(ext4_ext_test_block_flag(inode, iblock, BH_Delay) == 0){
> +                       get_blocks_flags = EXT4_GET_BLOCKS_CREATE | EXT4_GET_BLOCKS_DELALLOC_RESERVE;
> +                       ret = ext4_map_blocks(handle, inode, &map, get_blocks_flags);
> +                       /* If the blocks are found, release them */
> +
> +                       if(ret > 0){
> +                               num_blocks = ret;
> +                               ext4_ext_release_blocks(inode, iblock, iblock+num_blocks);
> +                               goto next;
> +                       }
> +               }
> +
> +               /* If the block cannot be identified, just skip it */
> +               num_blocks = 1;
> +
> +next:
> +               iblock+=num_blocks;
> +       }
> +       ext4_mark_inode_dirty(handle, inode);
> +
> +       ext4_journal_stop(handle);
> +
> +}
> +
>
>  static void ext4_falloc_update_inode(struct inode *inode,
>                                int mode, loff_t new_size, int update_ctime)
> @@ -4079,10 +4393,6 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
>        struct ext4_map_blocks map;
>        unsigned int credits, blkbits = inode->i_blkbits;
>
> -       /* We only support the FALLOC_FL_KEEP_SIZE mode */
> -       if (mode & ~FALLOC_FL_KEEP_SIZE)
> -               return -EOPNOTSUPP;
> -
>        /*
>         * currently supporting (pre)allocate mode for extent-based
>         * files _only_
> @@ -4090,6 +4400,9 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
>        if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)))
>                return -EOPNOTSUPP;
>
> +       if (mode & FALLOC_FL_PUNCH_HOLE)
> +               return ext4_punch_hole(inode, offset, len);
> +
>        map.m_lblk = offset >> blkbits;
>        /*
>         * We can't just convert len to max_blocks because
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 28c9137..493c908 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -4487,6 +4487,32 @@ int ext4_can_truncate(struct inode *inode)
>  }
>
>  /*
> + * ext4_punch_hole: punches a hole in a file by releaseing the blocks
> + * associated with the given offset and length
> + *
> + * @inode:  File inode
> + * @offset: The offset where the hole will begin
> + * @len:    The length of the hole
> + *
> + * Returns: 0 on sucess or negative on failure
> + */
> +
> +long  ext4_punch_hole(struct inode *inode, loff_t offset, loff_t length)
> +{
> +
> +       if (!S_ISREG(inode->i_mode)==1)
> +                return -ENOTSUPP;

(style) please drop the == 1. I am not even sure that !(0) is
guarantied to return 1...

> +
> +       if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
> +               //TODO: Add support for non extent hole punching
> +               return -ENOTSUPP;
> +       }
> +
> +       ext4_ext_punch_hole(inode, offset, length);
> +       return 0;
> +}
> +
> +/*
>  * ext4_truncate()
>  *
>  * We block out ext4_get_block() block instantiations across the entire
> --
> 1.7.1
>
>
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