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Re: [libvirt] [PATCH 7/8 v8] qemu: Set unpriv_sgio when attaching disk

On 2012年12月15日 06:05, Eric Blake wrote:
On 12/14/2012 08:45 AM, Osier Yang wrote:
Just like for domain starting, this sets the disk's unpriv_sgio
if cdbfilter is specified when attaching disk.
  src/qemu/qemu_driver.c |   23 +++++++++++++++++------
  1 files changed, 17 insertions(+), 6 deletions(-)

+        /* Set sysfs unpriv_sgio if cdbfilter is specified. */
+        if (disk->cdbfilter) {
+            if (virSetDeviceUnprivSGIO(disk->src, NULL,
+                                       (disk->cdbfilter ==
+                                       VIR_DOMAIN_DISK_CDB_FILTER_NO)
+                                       ? 1 : 0)<  0) {
+                VIR_WARN("Failed to set unpriv_sgio of disk '%s'", disk->src);
+                goto end;
+            }
+        }

Again, does this do the right thing if some other domain already had
cdbfilter='no' (aka kernel allows SG_IO) but this domain omitted the
cdbfilter attribute (which defaults to cdbfilter='yes' but does not
satisfy the if(disk->cdbfilter) condition)?

I think it does the right thing, because not specifying "cdbfilter"
should mean it doesn't care about what the kernel setting is, not
means cdbfiler="yes" instead. Assuming that one used rawio="yes"
for a domain, and if we defaults cdbfilter to "yes", it will cause
regression, as the user still expects SG_IO commands can be executed
on the disk, however, it's disabled by cdbfilter="yes".

 I suspect that will be
worked out when you rework things to use a tri-state rawio.

Of course, this is based on we use a separate XML tag like cdbfilter,
it won't stand anymore if we finally use a tri-state rawio.


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