On 03/02/2011 06:17 PM, Laine Stump wrote:
> On 03/02/2011 06:30 PM, Eric Blake wrote:
>> In virFileOperation, the parent does a fallback to a non-fork
>> attempt if it detects that the child returned EACCES. However,
>> the child was calling _exit(-EACCESS), which does _not_ appear
>> as EACCES in the parent.
>>
>> * src/util/util.c (virFileOperation): Correctly pass EACCES from
>> child to parent.
>> ---
>> src/util/util.c | 9 +++++++++
>> 1 files changed, 9 insertions(+), 0 deletions(-)
>>
>> diff --git a/src/util/util.c b/src/util/util.c
>> index bac71c8..0fe1c41 100644
>> --- a/src/util/util.c
>> +++ b/src/util/util.c
>> @@ -1559,6 +1559,15 @@ parenterror:
>> goto childerror;
>> }
>> childerror:
>> + /* Hook sets ret to -errno on failure, but exit must be positive.
>> + * If we exit with EACCES, then parent tries again. */
>> + /* XXX This makes assumptions about errno being< 255, which is
>> + * not true on Hurd. */
>> + ret = -ret;
>
> Maybe just a matter of taste, but I think I would prefer if everywhere
> in virFileOperation set ret = errno (instead of -errno), and when hook
> is called, do "ret = - hook(...)". Then you don't need the extra "ret =
> -ret".
Well, I thought about that, even before your comment. But considering
that parent does 'return ret', and was tracking ret = -errno everywhere,
I thought that tracking -errno in the parent and +errno in the child
half of the same function looked even weirder than just inverting errno
at the last second before _exit in the child.
>
> ACK either way, though.
I decided to keep it as-is, and pushed.
>
>> + if ((ret& 0xff) != ret) {
>> + VIR_WARN("unable to pass desired return value %d", ret);
Technically, calling VIR_WARN in a fork increases the chance of a
deadlock (if the virFork() was called while some other thread held the
malloc lock); but this is no worse than the fact that virFork is already
unsafe in the same manner; not to mention that this warning should never
trigger on Linux, where errno should always be in _exit() range. That
is, at some future point, we'll need to audit all uses of virFork for
async-signal safety, not just this point.
--
Eric Blake eblake@xxxxxxxxxx +1-801-349-2682
Libvirt virtualization library http://libvirt.org
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