| Message ID | 1383611706-22107-2-git-send-email-mreitz@redhat.com |
|---|---|
| State | New |
| Headers | show |
On 11/05/2013 08:35 AM, Max Reitz wrote: > It should be possible to execute the QMP "drive-mirror" command in > "none" sync mode and "absolute-paths" mode even for block devices > lacking a backing file. > > "absolute-paths" does in fact not require a backing file to be present, > as can be seen from the "top" sync mode code path. "top" basically > states that the device should indeed have a backing file - however, the > current code catches the case if it doesn't and then simply treats it as > "full" sync mode, creating a target image without a backing file (in > "absolute-paths" mode). Thus, "absolute-paths" does not imply the target > file must indeed have a backing file. > > Therefore, the target file may be left unbacked in case of "none" sync > mode as well, if the specified device is not backed either. Currently, > qemu will crash trying to dereference the backing file pointer since it > assumes that it will always be non-NULL in that case ("none" with > "absolute-paths"). > > Signed-off-by: Max Reitz <mreitz@redhat.com> > --- > blockdev.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/blockdev.c b/blockdev.c > index b260477..986e59d 100644 > --- a/blockdev.c > +++ b/blockdev.c > @@ -2038,8 +2038,8 @@ void qmp_drive_mirror(const char *device, const char *target, > case NEW_IMAGE_MODE_ABSOLUTE_PATHS: > /* create new image with backing file */ > bdrv_img_create(target, format, > - source->filename, > - source->drv->format_name, > + source ? source->filename : NULL, > + source ? source->drv->format_name : NULL, > NULL, size, flags, &local_err, false); > break; > default: The code around here is: 2029 if (sync == MIRROR_SYNC_MODE_FULL && mode != NEW_IMAGE_MODE_EXISTING) { 2030 /* create new image w/o backing file */ 2031 assert(format && drv); 2032 bdrv_img_create(target, format, 2033 NULL, NULL, NULL, size, flags, &local_err, false); 2034 } else { 2035 switch (mode) { 2036 case NEW_IMAGE_MODE_EXISTING: 2037 break; 2038 case NEW_IMAGE_MODE_ABSOLUTE_PATHS: 2039 /* create new image with backing file */ 2040 bdrv_img_create(target, format, 2041 source->filename, 2042 source->drv->format_name, 2043 NULL, size, flags, &local_err, false); 2044 break; 2045 default: 2046 abort(); 2047 } 2048 } Why not update the if condition and reuse the branch, I think this is a better branching? Either should be fine, but in your change you should also update the comment in line 2039. Thanks, Fam
On 05.11.2013 04:32, Fam Zheng wrote: > > On 11/05/2013 08:35 AM, Max Reitz wrote: >> It should be possible to execute the QMP "drive-mirror" command in >> "none" sync mode and "absolute-paths" mode even for block devices >> lacking a backing file. >> >> "absolute-paths" does in fact not require a backing file to be present, >> as can be seen from the "top" sync mode code path. "top" basically >> states that the device should indeed have a backing file - however, the >> current code catches the case if it doesn't and then simply treats it as >> "full" sync mode, creating a target image without a backing file (in >> "absolute-paths" mode). Thus, "absolute-paths" does not imply the target >> file must indeed have a backing file. >> >> Therefore, the target file may be left unbacked in case of "none" sync >> mode as well, if the specified device is not backed either. Currently, >> qemu will crash trying to dereference the backing file pointer since it >> assumes that it will always be non-NULL in that case ("none" with >> "absolute-paths"). >> >> Signed-off-by: Max Reitz <mreitz@redhat.com> >> --- >> blockdev.c | 4 ++-- >> 1 file changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/blockdev.c b/blockdev.c >> index b260477..986e59d 100644 >> --- a/blockdev.c >> +++ b/blockdev.c >> @@ -2038,8 +2038,8 @@ void qmp_drive_mirror(const char *device, const >> char *target, >> case NEW_IMAGE_MODE_ABSOLUTE_PATHS: >> /* create new image with backing file */ >> bdrv_img_create(target, format, >> - source->filename, >> - source->drv->format_name, >> + source ? source->filename : NULL, >> + source ? source->drv->format_name : NULL, >> NULL, size, flags, &local_err, false); >> break; >> default: > The code around here is: > > 2029 if (sync == MIRROR_SYNC_MODE_FULL && mode != > NEW_IMAGE_MODE_EXISTING) { > 2030 /* create new image w/o backing file */ > 2031 assert(format && drv); > 2032 bdrv_img_create(target, format, > 2033 NULL, NULL, NULL, size, flags, > &local_err, false); > 2034 } else { > 2035 switch (mode) { > 2036 case NEW_IMAGE_MODE_EXISTING: > 2037 break; > 2038 case NEW_IMAGE_MODE_ABSOLUTE_PATHS: > 2039 /* create new image with backing file */ > 2040 bdrv_img_create(target, format, > 2041 source->filename, > 2042 source->drv->format_name, > 2043 NULL, size, flags, &local_err, false); > 2044 break; > 2045 default: > 2046 abort(); > 2047 } > 2048 } > > Why not update the if condition and reuse the branch, I think this is > a better branching? Either should be fine, but in your change you > should also update the comment in line 2039. Okay, I'll go for updating the condition. Max > Thanks, > Fam
diff --git a/blockdev.c b/blockdev.c index b260477..986e59d 100644 --- a/blockdev.c +++ b/blockdev.c @@ -2038,8 +2038,8 @@ void qmp_drive_mirror(const char *device, const char *target, case NEW_IMAGE_MODE_ABSOLUTE_PATHS: /* create new image with backing file */ bdrv_img_create(target, format, - source->filename, - source->drv->format_name, + source ? source->filename : NULL, + source ? source->drv->format_name : NULL, NULL, size, flags, &local_err, false); break; default:
It should be possible to execute the QMP "drive-mirror" command in "none" sync mode and "absolute-paths" mode even for block devices lacking a backing file. "absolute-paths" does in fact not require a backing file to be present, as can be seen from the "top" sync mode code path. "top" basically states that the device should indeed have a backing file - however, the current code catches the case if it doesn't and then simply treats it as "full" sync mode, creating a target image without a backing file (in "absolute-paths" mode). Thus, "absolute-paths" does not imply the target file must indeed have a backing file. Therefore, the target file may be left unbacked in case of "none" sync mode as well, if the specified device is not backed either. Currently, qemu will crash trying to dereference the backing file pointer since it assumes that it will always be non-NULL in that case ("none" with "absolute-paths"). Signed-off-by: Max Reitz <mreitz@redhat.com> --- blockdev.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)