From: Tejun Heo Date: Fri, 1 Nov 2013 17:16:53 +0000 (-0400) Subject: sysfs: use generic_file_llseek() for sysfs_file_operations X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=044e3bc33391b1f2769d5ab2c04f246c3d8e04c3;p=GitHub%2FLineageOS%2FG12%2Fandroid_kernel_amlogic_linux-4.9.git 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 Reported-by: Heiko Carstens Link: https://lkml.kernel.org/r/20131031114358.GA5551@osiris Tested-by: Heiko Carstens Signed-off-by: Greg Kroah-Hartman --- 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,