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[Bug stdio/17830] New: dprintf fails when file descriptor is connected to /dev/kmsg
- From: "mac at mcrowe dot com" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sourceware dot org
- Date: Mon, 12 Jan 2015 12:33:16 +0000
- Subject: [Bug stdio/17830] New: dprintf fails when file descriptor is connected to /dev/kmsg
- Auto-submitted: auto-generated
https://sourceware.org/bugzilla/show_bug.cgi?id=17830
Bug ID: 17830
Summary: dprintf fails when file descriptor is connected to
/dev/kmsg
Product: glibc
Version: 2.21
Status: NEW
Severity: normal
Priority: P2
Component: stdio
Assignee: unassigned at sourceware dot org
Reporter: mac at mcrowe dot com
If the file descriptor passed to dprintf is connected to /dev/kmsg on a modern
Linux kernel then dprintf fails (apparently because /dev/kmsg does not support
seeking.)
Steps to reproduce:
1. Run a Linux kernel with new-style /dev/kmsg (I was running Debian Jessie's
v3.16 kernel but others as old as v3.8 show the same symptom.)
2. Compile the following code:
#include <stdio.h>
int main()
{
int r = dprintf(1, "test\n");
fprintf(stderr, "Result: %d %m\n", r);
return 0;
}
3. Run ./a.out and the result is as expected
test
Result: 5 Success
4. Run "./a.out >/dev/kmsg" and dprintf fails:
Result: -1 Bad file descriptor
and no output appears in the kernel log.
Expected result:
dprintf should work just as well on /dev/kmsg as anything else.
Reproduced in Debian Jessie's glibc v2.19 and glibc master at
56cf2763819d2f721c98f2b8bcc04a3c673837d3.
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