Messages in this thread Patch in this message | | | From | Vladimir Zapolskiy <> | Subject | [PATCH RESEND] fs: sysfs: return EFBIG on write if offset is larger than binary file size | Date | Thu, 9 Oct 2014 20:41:55 +0300 |
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According to the user expectations common utilities like dd or sh redirection operator '>' should work correctly over binary files from sysfs. At the moment doing excessive write can not be ever completed (no error is returned), e.g. for 4-byte file:
write(1, "\0\0\0\0\0\0\0\0", 8) = 4 write(1, "\0\0\0\0", 4) = 0 write(1, "\0\0\0\0", 4) = 0 write(1, "\0\0\0\0", 4) = 0 write(1, "\0\0\0\0", 4) = 0 write(1, "\0\0\0\0", 4) = 0 .......
This is not a successful completion of write(2), so fix the problem by returning EFBIG as described in POSIX.1-2001:
[EFBIG] The file is a regular file, nbyte is greater than 0, and the starting position is greater than or equal to the offset maximum established in the open file description associated with fildes.
Note, the write(2) ABI is changed, however 1) write(2) behaviour is corrected in conformance to POSIX, the existing userspace applications must be aware of possible errors on a syscall, 2) the return value is changed on error path, so it is an exceptional situation, 3) the change is related only to binary sysfs files, which is a very small class of files, mainly representing non-volatile registers or ram, eeproms etc, many of such files are read-only.
Presumably it is safe to apply the change, the described problem is definitely in the kernel and userspace utilities can not be changed to process 0 return value as an error, because it is just not an error according to POSIX.
Signed-off-by: Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Tejun Heo <tj@kernel.org> --- fs/sysfs/file.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c index e9ef59b..589abee 100644 --- a/fs/sysfs/file.c +++ b/fs/sysfs/file.c @@ -125,7 +125,7 @@ static ssize_t sysfs_kf_bin_write(struct kernfs_open_file *of, char *buf, if (size) { if (size <= pos) - return 0; + return -EFBIG; count = min_t(ssize_t, count, size - pos); } if (!count) -- 1.7.10.4
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