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vircommand: Make sysconf(_SC_OPEN_MAX) failure non-fatal

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The point of calling sysconf(_SC_OPEN_MAX) is to allocate big
enough bitmap so that subsequent call to
virCommandMassCloseGetFDsDir() can just set the bit instead of
expanding memory (this code runs in a forked off child and thus
using async-signal-unsafe functions like malloc() is a bit
tricky).

But on some systems the limit for opened FDs is virtually
non-existent (typically macOS Ventura started reporting EINVAL).

But with both glibc and musl using malloc() after fork() is safe.
And with sufficiently new glib too, as it's using malloc() with
newer releases instead of their own allocator.

Therefore, pick a sufficiently large value (glibc falls back to
256, [1], Darwin to 10240 [2] so 10240 should be good enough) to
fall back to and make the error non-fatal.

1: https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/getdtsz.c;h=4c5a6208067d2f9eaaac6dba652702fb4af9b7e3;hb=HEAD
2  https://github.com/apple/darwin-xnu/blob/main/bsd/sys/syslimits.h#L104

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Martin Kletzander <mkletzan@redhat.com>
This commit is contained in:
Michal Privoznik 2023-08-29 09:22:09 +02:00
parent 6ded014ba3
commit 4df8dc576f
1 changed files with 6 additions and 4 deletions
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10
src/util/vircommand.c
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@ -494,7 +494,7 @@ virCommandMassCloseGetFDsDir(virBitmap *fds,
return -1;
}
ignore_value(virBitmapSetBit(fds, fd));
virBitmapSetBitExpand(fds, fd);
}
if (rc < 0)
@ -539,9 +539,11 @@ virCommandMassCloseFrom(virCommand *cmd,
* Therefore we can safely allocate memory here (and transitively call
* opendir/readdir) without a deadlock. */
if (openmax < 0) {
virReportSystemError(errno, "%s", _("sysconf(_SC_OPEN_MAX) failed"));
return -1;
if (openmax <= 0) {
/* Darwin defaults to 10240. Start with a generous value.
* virCommandMassCloseGetFDsDir() uses virBitmapSetBitExpand() anyways.
*/
openmax = 10240;
}
fds = virBitmapNew(openmax);