Hey, Greg.
Here's proper patch with description and SOB. I'll be traveling from
tomorrow so I might not be responsive for some days. Can you please
apply it once Heiko confirms it fixes the issue?
Thanks!
------- 8< -------
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@xxxxxxxxxx>
Reported-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20131031114358.GA5551@osiris
---
fs/sysfs/file.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- 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,
--
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