| Message ID | 1461706338-20219-3-git-send-email-mreitz@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 04/26/2016 03:32 PM, Max Reitz wrote: > If the backing file is overridden, this most probably does change the > guest-visible data of a BDS. Therefore, we will need to consider this in > bdrv_refresh_filename(). > > Adding a new field to the BDS is not nice, but it is very simple and > exactly keeps track of whether the backing file has been overridden. > > Signed-off-by: Max Reitz <mreitz@redhat.com> > --- > block.c | 2 ++ > include/block/block_int.h | 1 + > 2 files changed, 3 insertions(+) Reviewed-by: Eric Blake <eblake@redhat.com>
Am 26.04.2016 um 23:32 hat Max Reitz geschrieben: > If the backing file is overridden, this most probably does change the > guest-visible data of a BDS. Therefore, we will need to consider this in > bdrv_refresh_filename(). > > Adding a new field to the BDS is not nice, but it is very simple and > exactly keeps track of whether the backing file has been overridden. > > Signed-off-by: Max Reitz <mreitz@redhat.com> What about live snapshots or block jobs that manipulate bs->backing? They don't use bdrv_open_backing_file(), but bdrv_append() or bdrv_replace_in_backing_chain() in order to assign a backing file, which may or may not be the same as in the image header. Also, do we want to consider a backing file overridden when the user specified it explicitly, but it matches the image header? Kevin > block.c | 2 ++ > include/block/block_int.h | 1 + > 2 files changed, 3 insertions(+) > > diff --git a/block.c b/block.c > index e349e83..e178488 100644 > --- a/block.c > +++ b/block.c > @@ -1299,6 +1299,7 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *parent_options, > > reference = qdict_get_try_str(parent_options, bdref_key); > if (reference || qdict_haskey(options, "file.filename")) { > + bs->backing_overridden = true; > backing_filename[0] = '\0'; > } else if (bs->backing_file[0] == '\0' && qdict_size(options) == 0) { > QDECREF(options); > @@ -1589,6 +1590,7 @@ static int bdrv_open_inherit(BlockDriverState **pbs, const char *filename, > backing = qdict_get_try_str(options, "backing"); > if (backing && *backing == '\0') { > flags |= BDRV_O_NO_BACKING; > + bs->backing_overridden = true; > qdict_del(options, "backing"); > } > > diff --git a/include/block/block_int.h b/include/block/block_int.h > index 10d8759..d73e9ce 100644 > --- a/include/block/block_int.h > +++ b/include/block/block_int.h > @@ -409,6 +409,7 @@ struct BlockDriverState { > char backing_file[PATH_MAX]; /* if non zero, the image is a diff of > this file image */ > char backing_format[16]; /* if non-zero and backing_file exists */ > + bool backing_overridden; /* backing file has been specified by the user */ > > QDict *full_open_options; > char exact_filename[PATH_MAX]; > -- > 2.8.0 >
On 02.05.2016 17:35, Kevin Wolf wrote: > Am 26.04.2016 um 23:32 hat Max Reitz geschrieben: >> If the backing file is overridden, this most probably does change the >> guest-visible data of a BDS. Therefore, we will need to consider this in >> bdrv_refresh_filename(). >> >> Adding a new field to the BDS is not nice, but it is very simple and >> exactly keeps track of whether the backing file has been overridden. >> >> Signed-off-by: Max Reitz <mreitz@redhat.com> > > What about live snapshots or block jobs that manipulate bs->backing? > They don't use bdrv_open_backing_file(), but bdrv_append() or > bdrv_replace_in_backing_chain() in order to assign a backing file, which > may or may not be the same as in the image header. I'll take a look into each case, thanks. > Also, do we want to consider a backing file overridden when the user > specified it explicitly, but it matches the image header? For simplicity's sake, I would. I think we've realized before that trying to identify whether to file names point to the same image is rather difficult. Max > > Kevin > >> block.c | 2 ++ >> include/block/block_int.h | 1 + >> 2 files changed, 3 insertions(+) >> >> diff --git a/block.c b/block.c >> index e349e83..e178488 100644 >> --- a/block.c >> +++ b/block.c >> @@ -1299,6 +1299,7 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *parent_options, >> >> reference = qdict_get_try_str(parent_options, bdref_key); >> if (reference || qdict_haskey(options, "file.filename")) { >> + bs->backing_overridden = true; >> backing_filename[0] = '\0'; >> } else if (bs->backing_file[0] == '\0' && qdict_size(options) == 0) { >> QDECREF(options); >> @@ -1589,6 +1590,7 @@ static int bdrv_open_inherit(BlockDriverState **pbs, const char *filename, >> backing = qdict_get_try_str(options, "backing"); >> if (backing && *backing == '\0') { >> flags |= BDRV_O_NO_BACKING; >> + bs->backing_overridden = true; >> qdict_del(options, "backing"); >> } >> >> diff --git a/include/block/block_int.h b/include/block/block_int.h >> index 10d8759..d73e9ce 100644 >> --- a/include/block/block_int.h >> +++ b/include/block/block_int.h >> @@ -409,6 +409,7 @@ struct BlockDriverState { >> char backing_file[PATH_MAX]; /* if non zero, the image is a diff of >> this file image */ >> char backing_format[16]; /* if non-zero and backing_file exists */ >> + bool backing_overridden; /* backing file has been specified by the user */ >> >> QDict *full_open_options; >> char exact_filename[PATH_MAX]; >> -- >> 2.8.0 >>
Am 03.05.2016 um 12:49 hat Max Reitz geschrieben: > On 02.05.2016 17:35, Kevin Wolf wrote: > > Am 26.04.2016 um 23:32 hat Max Reitz geschrieben: > >> If the backing file is overridden, this most probably does change the > >> guest-visible data of a BDS. Therefore, we will need to consider this in > >> bdrv_refresh_filename(). > >> > >> Adding a new field to the BDS is not nice, but it is very simple and > >> exactly keeps track of whether the backing file has been overridden. > >> > >> Signed-off-by: Max Reitz <mreitz@redhat.com> > > > > What about live snapshots or block jobs that manipulate bs->backing? > > They don't use bdrv_open_backing_file(), but bdrv_append() or > > bdrv_replace_in_backing_chain() in order to assign a backing file, which > > may or may not be the same as in the image header. > > I'll take a look into each case, thanks. > > > Also, do we want to consider a backing file overridden when the user > > specified it explicitly, but it matches the image header? > > For simplicity's sake, I would. I think we've realized before that > trying to identify whether to file names point to the same image is > rather difficult. I was just asking because in that case, we probably must consider things like the backing file of a live snapshot overlay overridden as well (at least when using an existing image). Kevin
diff --git a/block.c b/block.c index e349e83..e178488 100644 --- a/block.c +++ b/block.c @@ -1299,6 +1299,7 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *parent_options, reference = qdict_get_try_str(parent_options, bdref_key); if (reference || qdict_haskey(options, "file.filename")) { + bs->backing_overridden = true; backing_filename[0] = '\0'; } else if (bs->backing_file[0] == '\0' && qdict_size(options) == 0) { QDECREF(options); @@ -1589,6 +1590,7 @@ static int bdrv_open_inherit(BlockDriverState **pbs, const char *filename, backing = qdict_get_try_str(options, "backing"); if (backing && *backing == '\0') { flags |= BDRV_O_NO_BACKING; + bs->backing_overridden = true; qdict_del(options, "backing"); } diff --git a/include/block/block_int.h b/include/block/block_int.h index 10d8759..d73e9ce 100644 --- a/include/block/block_int.h +++ b/include/block/block_int.h @@ -409,6 +409,7 @@ struct BlockDriverState { char backing_file[PATH_MAX]; /* if non zero, the image is a diff of this file image */ char backing_format[16]; /* if non-zero and backing_file exists */ + bool backing_overridden; /* backing file has been specified by the user */ QDict *full_open_options; char exact_filename[PATH_MAX];
If the backing file is overridden, this most probably does change the guest-visible data of a BDS. Therefore, we will need to consider this in bdrv_refresh_filename(). Adding a new field to the BDS is not nice, but it is very simple and exactly keeps track of whether the backing file has been overridden. Signed-off-by: Max Reitz <mreitz@redhat.com> --- block.c | 2 ++ include/block/block_int.h | 1 + 2 files changed, 3 insertions(+)