[PATCH] Introduce SEEK_DATA/SEEK_HOLE support V8

Jeff Liu
2012-02-17T13:16:55Z

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@oracle.com>
---
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