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[PATCH] Introduce SEEK_DATA/SEEK_HOLE support V8

To: xfs@xxxxxxxxxxx
Subject: [PATCH] Introduce SEEK_DATA/SEEK_HOLE support V8
From: Jeff Liu <jeff.liu@xxxxxxxxxx>
Date: Fri, 17 Feb 2012 21:16:30 +0800
Cc: Ben Myers <bpm@xxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, Mark Tinguely <tinguely@xxxxxxx>, Dave Chinner <david@xxxxxxxxxxxxx>, Chris Mason <chris.mason@xxxxxxxxxx>
Organization: Oracle
Reply-to: jeff.liu@xxxxxxxxxx
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.18) Gecko/20110617 Thunderbird/3.1.11
Hello,

This is the revised patch according to Dave's comments for V7.

Changes to V8:
--------------
1. If there is an internal error raised at extent reading routine, just
return it rather than ENXIO.
2. Add the commit message.
3. Remove the for(;;) loop since there is no continuous holes shown even
if create a Petabyte sparse file with hole extent length longer than
32-bit.  Thanks Dave for helping verify that!
4. In xfs_seek_data(), s/len/end/, looks 'end' is more meaningful here
to indicate the range of extents mapped.
5. Remove BUG() from xfs_seek_data() since xfs_bmapi_read() have found
any corruption during the lookup, it should not occurred at all.

Any comments are appreciated!

Thanks,
-Jeff


Signed-off-by: Jie Liu <jeff.liu@xxxxxxxxxx>
---
 This patch adds lseek(2) SEEK_DATA/SEEK_HOLE functionality.

 fs/xfs/xfs_file.c |  135
++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 134 insertions(+), 1 deletions(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 753ed9b..1b3021c 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -1141,8 +1141,141 @@ xfs_vm_page_mkwrite(
        return block_page_mkwrite(vma, vmf, xfs_get_blocks);
 }

+STATIC loff_t
+xfs_seek_data(
+       struct file             *file,
+       loff_t                  start,
+       u32                     type)
+{
+       struct inode            *inode = file->f_mapping->host;
+       struct xfs_inode        *ip = XFS_I(inode);
+       struct xfs_mount        *mp = ip->i_mount;
+       struct xfs_bmbt_irec    map[2];
+       int                     nmap = 2;
+       loff_t                  uninitialized_var(offset);
+       xfs_fsize_t             isize;
+       xfs_fileoff_t           fsbno;
+       xfs_filblks_t           end;
+       uint                    lock;
+       int                     error;
+
+       lock = xfs_ilock_map_shared(ip);
+
+       isize = i_size_read(inode);
+       if (start >= isize) {
+               error = ENXIO;
+               goto out_unlock;
+       }
+
+       fsbno = XFS_B_TO_FSBT(mp, start);
+
+       /*
+        * Try to read extents from the first block indicated
+        * by fsbno to the end block of the file.
+        */
+       end = XFS_B_TO_FSB(mp, isize);
+
+       error = xfs_bmapi_read(ip, fsbno, end - fsbno, map, &nmap,
+                              XFS_BMAPI_ENTIRE);
+       if (error)
+               goto out_unlock;
+
+       /*
+        * Treat unwritten extent as data extent since it might
+        * contains dirty data in page cache.
+        */
+       if (map[0].br_startblock != HOLESTARTBLOCK) {
+               offset = max_t(loff_t, start,
+                              XFS_FSB_TO_B(mp, map[0].br_startoff));
+       } else {
+               if (nmap == 1) {
+                       error = ENXIO;
+                       goto out_unlock;
+               }
+
+               offset = max_t(loff_t, start,
+                              XFS_FSB_TO_B(mp, map[1].br_startoff));
+       }
+
+       if (offset != file->f_pos)
+               file->f_pos = offset;
+
+out_unlock:
+       xfs_iunlock_map_shared(ip, lock);
+
+       if (error)
+               return -error;
+       return offset;
+}
+
+STATIC loff_t
+xfs_seek_hole(
+       struct file             *file,
+       loff_t                  start,
+       u32                     type)
+{
+       struct inode            *inode = file->f_mapping->host;
+       struct xfs_inode        *ip = XFS_I(inode);
+       struct xfs_mount        *mp = ip->i_mount;
+       loff_t                  uninitialized_var(offset);
+       loff_t                  holeoff;
+       xfs_fsize_t             isize;
+       xfs_fileoff_t           fsbno;
+       uint                    lock;
+       int                     error;
+
+       lock = xfs_ilock_map_shared(ip);
+
+       isize = i_size_read(inode);
+       if (start >= isize) {
+               error = ENXIO;
+               goto out_unlock;
+       }
+
+       fsbno = XFS_B_TO_FSBT(mp, start);
+       error = xfs_bmap_first_unused(NULL, ip, 1, &fsbno, XFS_DATA_FORK);
+       if (error)
+               goto out_unlock;
+
+       holeoff = XFS_FSB_TO_B(mp, fsbno);
+       if (holeoff <= start)
+               offset = start;
+       else
+               offset = min_t(loff_t, holeoff, isize);
+
+       if (offset != file->f_pos)
+               file->f_pos = offset;
+
+out_unlock:
+       xfs_iunlock_map_shared(ip, lock);
+
+       if (error)
+               return -error;
+       return offset;
+}
+
+STATIC loff_t
+xfs_file_llseek(
+       struct file     *file,
+       loff_t          offset,
+       int             origin)
+{
+       switch (origin) {
+       case SEEK_END:
+       case SEEK_CUR:
+       case SEEK_SET:
+               return generic_file_llseek(file, offset, origin);
+       case SEEK_DATA:
+               return xfs_seek_data(file, offset, origin);
+       case SEEK_HOLE:
+               return xfs_seek_hole(file, offset, origin);
+       default:
+               return -EINVAL;
+       }
+}
+
 const struct file_operations xfs_file_operations = {
-       .llseek         = generic_file_llseek,
+       .llseek         = xfs_file_llseek,
        .read           = do_sync_read,
        .write          = do_sync_write,
        .aio_read       = xfs_file_aio_read,
-- 
1.7.9

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