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authorTejun Heo <tj@kernel.org>2013-11-01 13:16:53 -0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-11-01 12:13:37 -0700
commit044e3bc33391b1f2769d5ab2c04f246c3d8e04c3 (patch)
tree6f4d8ec0abfb0f47682e2d57e8ed2ae127474a07
parent1c1365e374bfadf908eae02cded7abb9e672c9d4 (diff)
downloadlinux-044e3bc33391b1f2769d5ab2c04f246c3d8e04c3.tar.bz2
sysfs: use generic_file_llseek() for sysfs_file_operations
13c589d5b0ac6 ("sysfs: use seq_file when reading regular files") converted regular sysfs files to use seq_file. The commit substituted generic_file_llseek() with seq_lseek() for llseek implementation. Before the change, all regular sysfs files were allowed to seek to any position in [0, PAGE_SIZE] as the file size is always PAGE_SIZE and generic_file_llseek() allows any seeking inside the range under file size; however, seq_lseek()'s behavior is different. It traverses the output by repeatedly invoking ->show() until it reaches the target offset or traversal indicates EOF. As seq_files are fully dynamic and may not end at all, it doesn't support seeking from the end (SEEK_END). Apparently, there are userland tools which uses SEEK_END to discover the buffer size to use and the switch to seq_lseek() disturbs them as SEEK_END fails with -EINVAL. The only benefits of using seq_lseek() instead of generic_file_llseek() are * Early failure. If traversing to certain file position should fail, seq_lseek() will report such failures on lseek(2) instead of the following read/write operations. * EOF detection. While SEEK_END is not supported, SEEK_SET/CUR + large offset can be used to detect eof - eof at the time of the seek anyway as the file size may change dynamically. Both aren't necessary for sysfs or prospect kernfs users. Revert to genefic_file_llseek() and preserve the original behavior. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Heiko Carstens <heiko.carstens@de.ibm.com> Link: https://lkml.kernel.org/r/20131031114358.GA5551@osiris Tested-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--fs/sysfs/file.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index 382db3c045f3..79b5da2acbe1 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -800,7 +800,7 @@ EXPORT_SYMBOL_GPL(sysfs_notify);
const struct file_operations sysfs_file_operations = {
.read = seq_read,
.write = sysfs_write_file,
- .llseek = seq_lseek,
+ .llseek = generic_file_llseek,
.open = sysfs_open_file,
.release = sysfs_release,
.poll = sysfs_poll,