Hi, [replying to this version because the previous mail doesn't seem to have made it to the mailing lists for whatever reason]
On 2018-05-02 15:34, Ivan Ren wrote: > qemu-img info with a block device which has a qcow2 format always > return 0 for disk size, and this can not reflect the qcow2 size > and the used space of the block device. This patch return the > allocated size of qcow2 as the disk size. I'm not quite sure whether you really need this information for block devices (I tend to agree with Eric that wr_highest_cluster is the more important information there), but I can imagine it just being nice to have. So the basic idea makes sense to me, but I think the implementation can be simplified and the reporting in qemu-img should be done differently. > > Signed-off-by: Ivan Ren <ivan...@tencent.com> > --- > block/qcow2-bitmap.c | 69 +++++++++++++++++ > block/qcow2.c | 212 > +++++++++++++++++++++++++++++++++++++++++++++++++++ > block/qcow2.h | 42 ++++++++++ > 3 files changed, 323 insertions(+) The whole implementation reminds me a lot of qcow2's check function, which basically just recalculates the refcounts. So I'm wondering whether you could just count how many clusters with non-0 refcount there are and thus simplify the implementation dramatically. [...] > +static int64_t qcow2_get_allocated_file_size(BlockDriverState *bs) > +{ > + struct stat st; > + if (stat(bs->filename, &st) < 0 || !S_ISBLK(st.st_mode)) { > + goto get_file_size; > + } This definitely doesn't work because nobody guarantees that bs->filename is something that stat() can work with. I'm aware that you need to do the S_ISBLK() check somewhere, but the qcow2 driver is not the right place. I don't really have a good way around this, though. These things come to mind: (1) We could let file-posix report an error for S_ISBLK because the information is known to be usually useless -- but I think that is not quite the right thing to do because maybe some block devices do report useful information there, I don't know. (2) Or we introduce a new field in qemu-img info (and thus in ImageInfo, too, I suppose?). qemu-img info (or rather bdrv_query_image_info()) could detect whether the format layer supports bdrv_get_allocated_file_size, and if so, it emits that information separately from the allocated size of bs->file->bs. But that would break vmdk... (3) As a hack, qcow2_get_allocated_file_size() could first always call bdrv_get_allocated_file_size(bs->file->bs), and if that returns 0 (which is absolutely impossible for qcow2 files because they have an image header that takes up some space), we fall back to qcow2_get_block_allocated_size(). While I consider it a hack, I can't come up with a scenario where it wouldn't work. Max > + > + return qcow2_get_block_allocated_size(bs); > + > +get_file_size: > + if (bs->file) { > + return bdrv_get_allocated_file_size(bs->file->bs); > + } > + return -ENOTSUP; > +} > +
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