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[PATCH] Introduce SEEK_DATA/SEEK_HOLE support to XFS V6

To: xfs@xxxxxxxxxxx
Subject: [PATCH] Introduce SEEK_DATA/SEEK_HOLE support to XFS V6
From: Jeff Liu <jeff.liu@xxxxxxxxxx>
Date: Sun, 29 Jan 2012 16:35:41 +0800
Cc: Ben Myers <bpm@xxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, Mark Tinguely <tinguely@xxxxxxx>, 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,

Sorry for the delay!! I just got back from vacation.

This is the V6 to introduce SEEK_DATA/SEEK_HOLE support to XFS.
As we have discussed previously, I have removed the dirty data probing stuff 
and just treating unwritten extents as data in this post.

Changes to V6:
--------------
* remove xfs_has_unwritten_buffer() for now.
* xfs_bmapi_read() returns the br_state == XFS_EXT_NORM for a hole, so we need 
to check its startblock is not a "nullstartblock" in this case.
* call i_size_read() after taking the ilock shared, otherwise, isize could be 
stale.
* remove "ifp = XFS_IFORK_PTR(ip, XFS_DATA_FORK)" from xfs_seek_data() since it 
will not used.
* in xfs_file_llseek(), return -EINVAL rather than -EOPNOTSUPP if whence is not 
valid according to http://linux.die.net/man/2/lseek.
* s/int lock/uint lock/ in both xfs_seek_data() and xfs_seek_hole().
* s/out_lock/out_unlock/ in both functions too.

Tests:
------
* seek_sanity_tester:
http://permalink.gmane.org/gmane.comp.file-systems.xfs.general/42514

*seek_copy_tester:
http://permalink.gmane.org/gmane.comp.file-systems.xfs.general/42522


Thank you!
-Jeff


Signed-off-by: Jie Liu <jeff.liu@xxxxxxxxxx>

---
 fs/xfs/xfs_file.c |  168 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 167 insertions(+), 1 deletions(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 753ed9b..41a045f 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -1141,8 +1141,174 @@ 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;
+       loff_t                  uninitialized_var(offset);
+       xfs_fsize_t             isize;
+       xfs_fileoff_t           fsbno;
+       xfs_filblks_t           len;
+       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);
+       len = XFS_B_TO_FSB(mp, isize);
+       for (;;) {
+               struct xfs_bmbt_irec    map[2];
+               int                     nmap = 2;
+               loff_t                  seekoff;
+
+               error = xfs_bmapi_read(ip, fsbno, len - fsbno, map, &nmap,
+                                      XFS_BMAPI_ENTIRE);
+               if (error)
+                       goto out_unlock;
+
+               /* No extents at given offset, must be beyond EOF */
+               if (nmap == 0) {
+                       error = ENXIO;
+                       goto out_unlock;
+               }
+
+               seekoff = XFS_FSB_TO_B(mp, fsbno);
+
+               if ((map[0].br_state == XFS_EXT_NORM &&
+                    !isnullstartblock(map[0].br_startblock)) ||
+                   map[0].br_startblock == DELAYSTARTBLOCK) {
+                       offset = max_t(loff_t, seekoff,
+                                      XFS_FSB_TO_B(mp, map[0].br_startoff));
+                       break;
+               } else if (map[0].br_state == XFS_EXT_UNWRITTEN) {
+                       offset = max_t(loff_t, seekoff,
+                                      XFS_FSB_TO_B(mp, map[0].br_startoff));
+                       break;
+               } else if (map[0].br_startblock == HOLESTARTBLOCK) {
+                       if (nmap == 1) {
+                               error = ENXIO;
+                               goto out_unlock;
+                       }
+
+                       if ((map[1].br_state == XFS_EXT_NORM &&
+                            !isnullstartblock(map[1].br_startblock)) ||
+                           map[1].br_startblock == DELAYSTARTBLOCK) {
+                               offset = max_t(loff_t, seekoff,
+                                       XFS_FSB_TO_B(mp, map[1].br_startoff));
+                               break;
+                       } else if (map[1].br_state == XFS_EXT_UNWRITTEN) {
+                               offset = max_t(loff_t, seekoff,
+                                       XFS_FSB_TO_B(mp, map[1].br_startoff));
+                               break;
+                       } else if (map[1].br_startblock == HOLESTARTBLOCK) {
+                               fsbno = map[1].br_startoff +
+                                       map[1].br_blockcount;
+                       } else {
+                               BUG();
+                       }
+               } else {
+                       BUG();
+               }
+
+               if (XFS_FSB_TO_B(mp, fsbno) > isize) {
+                       error = ENXIO;
+                       goto out_unlock;
+               }
+       }
+
+       if (offset < start)
+               offset = start;
+
+       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,
-- 
1.7.4.1

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