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Re: [libvirt] [PATCHv4 06/15] qemu: allow simple domain save to use fd: protocol



On 03/10/2011 05:05 AM, Daniel P. Berrange wrote:
> On Wed, Mar 09, 2011 at 06:45:46PM -0700, Eric Blake wrote:
>> This allows direct saves (no compression, no root-squash NFS) to use
>> the more efficient fd: migration, which in turn avoids a race where
>> qemu exec: migration can sometimes fail because qemu does a generic
>> waitpid() that conflicts with the pclose() used by exec:.  Further
>> patches will solve compression and root-squash NFS.
>>
>> * src/qemu/qemu_driver.c (qemudDomainSaveFlag): Use new function
>> when there is no compression.
>> ---
>>  src/qemu/qemu_driver.c |   26 +++++++++++++++++++++++---
>>  1 files changed, 23 insertions(+), 3 deletions(-)
>>
>> +        /* XXX gross - why don't we reuse the fd already opened earlier */
>> +        int fd = -1;
>> +
>> +        if (qemuCapsGet(qemuCaps, QEMU_CAPS_MIGRATE_QEMU_FD) &&
>> +            priv->monConfig->type == VIR_DOMAIN_CHR_TYPE_UNIX)
>> +            fd = open(path, O_WRONLY);
> 
> Ok, so this is the bit which causes a regression on NFS rootsquash,
> if the path isn't readable by root.

Nope; no regression - just no fd: migration (it's a graceful fallback to
exec: migration on NFS rootsquash until later patches in the series).

> 
>>          qemuDomainObjEnterMonitorWithDriver(driver, vm);
>> -        rc = qemuMonitorMigrateToFile(priv->mon,
>> -                                      QEMU_MONITOR_MIGRATE_BACKGROUND,
>> -                                      args, path, offset);
>> +        if (fd >= 0 && lseek(fd, offset, SEEK_SET) == offset) {
>> +            rc = qemuMonitorMigrateToFd(priv->mon,
>> +                                        QEMU_MONITOR_MIGRATE_BACKGROUND,
>> +                                        fd);
>> +        } else {
>> +            rc = qemuMonitorMigrateToFile(priv->mon,
>> +                                          QEMU_MONITOR_MIGRATE_BACKGROUND,
>> +                                          args, path, offset);
>> +        }
>> +        VIR_FORCE_CLOSE(fd);

Did this patch get ACK? I'm thinking of shuffling things and pushing
this prior to 5/15 (introduction of SCM_RIGHTS); patch 5 and 6 have no
direct influence on one another.

But I'm also annoyed at having to open qemuCaps, and am thinking about
fixing that first.

-- 
Eric Blake   eblake redhat com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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