From: "Dmitry V. Levin" <ldv@altlinux.org>
To: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
linux-api@vger.kernel.org, linux-kernel@vger.kernel.org,
mtk.manpages@gmail.com
Subject: [PATCH v2] uapi: change the type of struct statx_timestamp.tv_nsec to unsigned
Date: Wed, 26 Apr 2017 14:19:07 +0300 [thread overview]
Message-ID: <20170426111907.GA7231@altlinux.org> (raw)
In-Reply-To: <13744.1493204125@warthog.procyon.org.uk>
The comment asserting that the value of struct statx_timestamp.tv_nsec
must be negative when statx_timestamp.tv_sec is negative, is wrong, as
could be seen from the following example:
#define _FILE_OFFSET_BITS 64
#include <assert.h>
#include <fcntl.h>
#include <stdio.h>
#include <sys/stat.h>
#include <unistd.h>
#include <asm/unistd.h>
#include <linux/stat.h>
int main(void)
{
static const struct timespec ts[2] = {
{ .tv_nsec = UTIME_OMIT },
{ .tv_sec = -2, .tv_nsec = 42 }
};
assert(utimensat(AT_FDCWD, ".", ts, 0) == 0);
struct stat st;
assert(stat(".", &st) == 0);
printf("st_mtim.tv_sec = %lld, st_mtim.tv_nsec = %lu\n",
(long long) st.st_mtim.tv_sec,
(unsigned long) st.st_mtim.tv_nsec);
struct statx stx;
assert(syscall(__NR_statx, AT_FDCWD, ".", 0, 0, &stx) == 0);
printf("stx_mtime.tv_sec = %lld, stx_mtime.tv_nsec = %lu\n",
(long long) stx.stx_mtime.tv_sec,
(unsigned long) stx.stx_mtime.tv_nsec);
return 0;
}
It expectedly prints:
st_mtim.tv_sec = -2, st_mtim.tv_nsec = 42
stx_mtime.tv_sec = -2, stx_mtime.tv_nsec = 42
The more generic comment asserting that the value of struct
statx_timestamp.tv_nsec might be negative is confusing to say the least.
It contradicts both the struct stat.st_[acm]time_nsec tradition and
struct timespec.tv_nsec requirements in utimensat syscall.
If statx syscall ever returns a stx_[acm]time containing a negative
tv_nsec that cannot be passed unmodified to utimensat syscall,
it will cause an immense confusion.
Fix this source of confusion by changing the type of struct
statx_timestamp.tv_nsec from __s32 to __u32.
Fixes: a528d35e8bfc ("statx: Add a system call to make enhanced file info available")
Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
---
v1: fix misleading comments
v2: change the type from __s32 to __u32
---
include/uapi/linux/stat.h | 8 ++------
1 file changed, 2 insertions(+), 6 deletions(-)
diff --git a/include/uapi/linux/stat.h b/include/uapi/linux/stat.h
index d538897..17b1030 100644
--- a/include/uapi/linux/stat.h
+++ b/include/uapi/linux/stat.h
@@ -48,17 +48,13 @@
* tv_sec holds the number of seconds before (negative) or after (positive)
* 00:00:00 1st January 1970 UTC.
*
- * tv_nsec holds a number of nanoseconds before (0..-999,999,999 if tv_sec is
- * negative) or after (0..999,999,999 if tv_sec is positive) the tv_sec time.
- *
- * Note that if both tv_sec and tv_nsec are non-zero, then the two values must
- * either be both positive or both negative.
+ * tv_nsec holds a number of nanoseconds (0..999,999,999) after the tv_sec time.
*
* __reserved is held in case we need a yet finer resolution.
*/
struct statx_timestamp {
__s64 tv_sec;
- __s32 tv_nsec;
+ __u32 tv_nsec;
__s32 __reserved;
};
--
ldv
prev parent reply other threads:[~2017-04-26 11:19 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-22 19:27 [PATCH] uapi: remove false assertion that statx_timestamp.tv_nsec can be negative Dmitry V. Levin
2017-04-26 10:55 ` David Howells
2017-04-26 11:19 ` Dmitry V. Levin [this message]
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