diff options
| author | Bruno Meneguele <bmeneg@redhat.com> | 2020-03-17 07:33:44 -0300 |
|---|---|---|
| committer | Petr Mladek <pmladek@suse.com> | 2020-05-21 13:32:25 +0200 |
| commit | 8ece3b3eb576a78d2e67ad4c3a80a39fa6708809 (patch) | |
| tree | adbc01ab55fd5dd70eb61e77391fa002670490c6 /Documentation | |
| parent | 325606af573152e02f44d791f152b7f9564bcb30 (diff) | |
kernel/printk: add kmsg SEEK_CUR handling
Userspace libraries, e.g. glibc's dprintf(), perform a SEEK_CUR operation
over any file descriptor requested to make sure the current position isn't
pointing to junk due to previous manipulation of that same fd. And whenever
that fd doesn't have support for such operation, the userspace code expects
-ESPIPE to be returned.
However, when the fd in question references the /dev/kmsg interface, the
current kernel code state returns -EINVAL instead, causing an unexpected
behavior in userspace: in the case of glibc, when -ESPIPE is returned it
gets ignored and the call completes successfully, while returning -EINVAL
forces dprintf to fail without performing any action over that fd:
if (_IO_SEEKOFF (fp, (off64_t)0, _IO_seek_cur, _IOS_INPUT|_IOS_OUTPUT) ==
_IO_pos_BAD && errno != ESPIPE)
return NULL;
With this patch we make sure to return the correct value when SEEK_CUR is
requested over kmsg and also add some kernel doc information to formalize
this behavior.
Link: https://lore.kernel.org/r/20200317103344.574277-1-bmeneg@redhat.com
Cc: linux-kernel@vger.kernel.org
Cc: rostedt@goodmis.org,
Cc: David.Laight@ACULAB.COM
Signed-off-by: Bruno Meneguele <bmeneg@redhat.com>
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/ABI/testing/dev-kmsg | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/Documentation/ABI/testing/dev-kmsg b/Documentation/ABI/testing/dev-kmsg index f307506eb54c..1e6c28b1942b 100644 --- a/Documentation/ABI/testing/dev-kmsg +++ b/Documentation/ABI/testing/dev-kmsg @@ -56,6 +56,11 @@ Description: The /dev/kmsg character device node provides userspace access seek after the last record available at the time the last SYSLOG_ACTION_CLEAR was issued. + Due to the record nature of this interface with a "read all" + behavior and the specific positions each seek operation sets, + SEEK_CUR is not supported, returning -ESPIPE (invalid seek) to + errno whenever requested. + The output format consists of a prefix carrying the syslog prefix including priority and facility, the 64 bit message sequence number and the monotonic timestamp in microseconds, |