Hello,
First,
Attached is a patch that adds errno information to 'write error' messages, e.g.:
$ grep [...] > /dev/full
grep: write error: No space left on device
I hope it is self-explanatory enough (comments and suggestions are welcomed).
Second,
On one gnu/linux server I'm experiencing a strange behavior (or at least, not
understandable to me):
grep does not immediately terminates on SIGPIPE, and instead exits and prints "write
error" (for EPIPE).
which is partially why I wrote the above patch, to try understand what's going
on.
An example, reproducible on my machine (running on real hardware), though hard
to reproduce inside a VM and on other servers:
seq 100000 > in
for i in $(seq 100) ; do
./src/grep -s --line-buffered -v '^$' < in | head -n1 > /dev/null ;
done
for some of the runs (out of 100) I get an error "./src/grep: write error: Broken
pipe" .
attached are strace/ltrace logs of such cases. the key lines:
When grep is killed by SIGPIPE:
== strace ==
write(1, "1\n", 2) = 2
write(1, "2\n", 2) = -1 EPIPE (Broken pipe)
--- SIGPIPE {si_signo=SIGPIPE, si_code=SI_USER, si_pid=2960, si_uid=1004} ---
+++ killed by SIGPIPE +++
== ltrace ==
fwrite_unlocked("1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n11\n12\n13\n14"..., 1, 2,
0x7efc5dab9400) = 2
__errno_location()
= 0x7efc5dee46a0
fflush_unlocked(0x7efc5dab9400, 0x18da000, 10, 4096)
= 0
memchr("2\n3\n4\n5\n6\n7\n8\n9\n10\n11\n12\n13\n14\n1"..., '\n', 32766)
= 0x18da003
fwrite_unlocked("2\n3\n4\n5\n6\n7\n8\n9\n10\n11\n12\n13\n14\n1"..., 1, 2,
0x7efc5dab9400) = 2
__errno_location()
= 0x7efc5dee46a0
fflush_unlocked(0x7efc5dab9400, 0x18da004, 0, 2610 <no return ...>
--- SIGPIPE (Broken pipe) ---
+++ killed by SIGPIPE +++
When grep is not killed by SIGPIPE:
== strace ==
write(1, "1\n", 2) = 2
write(1, "2\n", 2) = -1 EPIPE (Broken pipe)
--- SIGPIPE {si_signo=SIGPIPE, si_code=SI_USER, si_pid=2893, si_uid=1004} ---
write(2, "./src/grep: ", 12) = 12
write(2, "write error", 11) = 11
write(2, ": Broken pipe", 13) = 13
write(2, "\n", 1) = 1
exit_group(2) = ?
== ltrace ==
fwrite_unlocked("1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n11\n12\n13\n14"..., 1, 2,
0x7f9e62f50400) = 2
__errno_location()
= 0x7f9e6337b6a0
fflush_unlocked(0x7f9e62f50400, 0x25af000, 10, 4096)
= 0
memchr("2\n3\n4\n5\n6\n7\n8\n9\n10\n11\n12\n13\n14\n1"..., '\n', 32766)
= 0x25af003
fwrite_unlocked("2\n3\n4\n5\n6\n7\n8\n9\n10\n11\n12\n13\n14\n1"..., 1, 2,
0x7f9e62f50400) = 2
__errno_location()
= 0x7f9e6337b6a0
fflush_unlocked(0x7f9e62f50400, 0x25af004, 0, 2610 <no return ...>
--- SIGPIPE (Broken pipe) ---
<... fflush_unlocked resumed> )
= 0xffffffff
__errno_location()
= 0x7f9e6337b6a0
error(2, 32, 0x41caa0, 32 <no return ...>
The server is:
$ uname -a
Linux x 3.13.0-77-generic #121-Ubuntu SMP Wed Jan 20 10:50:42 UTC 2016 x86_64
GNU/Linux
$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc/x86_64-unknown-linux-gnu/5.2.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-5.2.0/configure --enable-languages=c,c++
Thread model: posix
gcc version 5.2.0 (GCC)
Thanks for any feedback,
regards,
- assaf
grep-write-error-msg.patch.xz
Description: application/xz
grep-SIGPIPE-killed.ltrace.log.xz
Description: application/xz
grep-SIGPIPE-killed.strace.log.xz
Description: application/xz
grep-SIGPIPE-not-killed.ltrace.log.xz
Description: application/xz
grep-SIGPIPE-not-killed.strace.log.xz
Description: application/xz
