On 12.03.2019 3:00, Eric Blake wrote: > On 3/11/19 1:51 PM, Vladimir Sementsov-Ogievskiy wrote: >> We already use (we didn't notice it) IN_USE flag for marking bitmap >> metadata outdated, such as AUTO flag, which mirrors enabled/disabled >> bitmaps. No we are going to support bitmap resize, so it's good to > > s/No/Now/ > >> write IN_USE meaning with more details. >> >> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com> >> --- >> docs/interop/qcow2.txt | 18 +++++++++++++++--- >> 1 file changed, 15 insertions(+), 3 deletions(-) >> >> diff --git a/docs/interop/qcow2.txt b/docs/interop/qcow2.txt >> index fb5cb47245..575a5f25e2 100644 >> --- a/docs/interop/qcow2.txt >> +++ b/docs/interop/qcow2.txt >> @@ -589,7 +589,19 @@ Structure of a bitmap directory entry: >> Bit >> 0: in_use >> The bitmap was not saved correctly and may be >> - inconsistent. >> + inconsistent. This inconsitency may touch both >> bitmap > > inconsistency > >> + data and metadata, and this mean that bitmap state >> + (its data and metadata) was changed but not stored >> + back to the image. This flag doesn't relate to >> format >> + corruption, all fields are still correct from qcow2 >> + point of view, they just may be outdated. >> + >> + Note: Currently, Qemu may change (additionally to >> + bitmap data) @auto flag and size of the bitmap >> during >> + image resize. This mean, that not only bitmap data >> + may be outdated if @in_use flag set, but also >> value of >> + @auto flag and bitmap size (which is indirectly >> + referenced by @bitmap_table_size). > > Feels wordy. Maybe drop the second paragraph starting with Note, and > merely use this for the first paragraph: > > The bitmap was not saved correctly and may be inconsistent. Although the > bitmap metadata is still well-formed from a qcow2 perspective, the > metadata (such as the auto flag or bitmap size) or data contents may be > outdated.
Sounds good (as always), thanks) > >> >> 1: auto >> The bitmap must reflect all changes of the virtual >> @@ -717,8 +729,8 @@ corresponding range of the virtual disk (see above) was >> written to while the >> bitmap was 'enabled'. An unset bit means that this range was not written >> to. >> >> The software doesn't have to sync the bitmap in the image file with its >> -representation in RAM after each write. Flag 'in_use' should be set while >> the >> -bitmap is not synced. >> +representation in RAM after each write or metadata change. Flag 'in_use' >> +should be set while the bitmap is not synced. >> >> In the image file the 'enabled' state is reflected by the 'auto' flag. If >> this >> flag is set, the software must consider the bitmap as 'enabled' and start >> >
