On Thu, Dec 29, 2011 at 05:36:59PM +0800, Dong Xu Wang wrote: > From: Dong Xu Wang <wdon...@linux.vnet.ibm.com> > > Introduce a new file format: add-cow. The usage can be found in add-cow.txt of > this patch. > > CC: Kevin Wolf <kw...@redhat.com> > CC: Stefan Hajnoczi <stefa...@linux.vnet.ibm.com> > Signed-off-by: Dong Xu Wang <wdon...@linux.vnet.ibm.com> > --- > After applying this patch, qemu might can not compile, need apply this patch > first: > http://lists.gnu.org/archive/html/qemu-devel/2011-12/msg02527.html > > Makefile.objs | 1 + > block.c | 2 +- > block.h | 1 + > block/add-cow.c | 429 > ++++++++++++++++++++++++++++++++++++++++++++++++ > block_int.h | 1 + > docs/specs/add-cow.txt | 72 ++++++++ > 6 files changed, 505 insertions(+), 1 deletions(-) > create mode 100644 block/add-cow.c > create mode 100644 docs/specs/add-cow.txt >
> + s->bitmap_size = ((bs->total_sectors + 7) >> 3); > + s->bitmap = qemu_blockalign(bs, s->bitmap_size); > + > + ret = bdrv_pread(bs->file, sizeof(header), s->bitmap, > + s->bitmap_size); > + if (ret != s->bitmap_size) { > + goto fail; > + } As noted previously, it is not acceptable to read the entire bitmap in memory since it might be very large. A cache, which limits the in-memory size of the bitmap, must be created. In the qcow2-cache.c file you can find an example (thats for qcow2 metadata cache). You can divide the bitmap in chunks of say, 4k, and have: int is_bit_set(int64_t bitnum, BlockDriverState *bs) { int64_t bitmap_entry = bitnum >> bits_per_entry; if (!is_in_bitmap_cache(bs, bitmap_entry)) read_from_disk(bs, bitmap_entry); return lookup_bitmap_cache(bs, bitnum); } And then limit the cache to a few megabytes. Also when setting a bit you must update cache and write to disk. > + > + if (s->image_file[0] == '\0') { > + ret = -ENOENT; > + goto fail; > + } > + > + ret = bdrv_file_open(&backing_bs, bs->backing_file, 0); > + if (ret < 0) { > + return ret; > + } > + bdrv_delete(backing_bs); > + > + s->image_hd = bdrv_new(""); > + > + if (path_has_protocol(s->image_file)) { > + pstrcpy(image_filename, sizeof(image_filename), > + s->image_file); > + } else { > + path_combine(image_filename, sizeof(image_filename), > + bs->filename, s->image_file); > + } > + > + image_drv = bdrv_find_format("raw"); > + ret = bdrv_open(s->image_hd, image_filename, flags, image_drv); > + if (ret < 0) { > + bdrv_delete(s->image_hd); > + s->image_hd = NULL; > + goto fail; > + } Please make sure it is possible to create a snapshot with the snapshot_blkdev command, of a raw image. It is necessary for live block copy, as described here: http://patchwork.ozlabs.org/patch/134257/ Also please update that document, later, with raw examples. Thanks