On 06.09.2010, at 12:04, Stefan Hajnoczi wrote: > QEMU Enhanced Disk format is a disk image format that forgoes features > found in qcow2 in favor of better levels of performance and data > integrity. Due to its simpler on-disk layout, it is possible to safely > perform metadata updates more efficiently. > > Installations, suspend-to-disk, and other allocation-heavy I/O workloads > will see increased performance due to fewer I/Os and syncs. Workloads > that do not cause new clusters to be allocated will perform similar to > raw images due to in-memory metadata caching. > > The format supports sparse disk images. It does not rely on the host > filesystem holes feature, making it a good choice for sparse disk images > that need to be transferred over channels where holes are not supported. > > Backing files are supported so only deltas against a base image can be > stored. > > The file format is extensible so that additional features can be added > later with graceful compatibility handling. > > Internal snapshots are not supported. This eliminates the need for > additional metadata to track copy-on-write clusters. > > Compression and encryption are not supported. They add complexity and > can be implemented at other layers in the stack (i.e. inside the guest > or on the host). > > The format is currently functional with the following features missing: > * Resizing the disk image. The capability has been designed in but the > code has not been written yet. > * Resetting the image after backing file commit completes. > * Changing the backing filename. > * Consistency check (fsck). This is simple due to the on-disk layout.
Yippie - yet another disk format :). Let's hope this one survives. > > Signed-off-by: Anthony Liguori <aligu...@us.ibm.com> > Signed-off-by: Stefan Hajnoczi <stefa...@linux.vnet.ibm.com> > --- > This code is also available from git (for development and testing the tracing > and blkverify features are pulled in, whereas this single squashed patch > applies to mainline qemu.git): > > http://repo.or.cz/w/qemu/stefanha.git/shortlog/refs/heads/qed > just looked at it and stumbled over two simple nits. [snip] > +/** > + * Get the number of bits for a power of 2 > + * > + * The following is true for powers of 2: > + * n == 1 << get_bits_from_size(n) > + */ > +int get_bits_from_size(size_t size) > +{ > + int res = 0; > + > + if (size == 0) { > + return -1; > + } > + > + while (size != 1) { > + /* Not a power of two */ > + if (size & 1) { > + return -1; > + } > + > + size >>= 1; > + res++; > + } > + > + return res; > +} Should be an extra patch - it doesn't hurt to send an RFC patch set. This thing is so big that it's no fun to review :). > + > +const char *bytes_to_str(uint64_t size) > +{ > + static char buffer[64]; > + > + if (size < (1ULL << 10)) { > + snprintf(buffer, sizeof(buffer), "%" PRIu64 " byte(s)", size); > + } else if (size < (1ULL << 20)) { > + snprintf(buffer, sizeof(buffer), "%" PRIu64 " KB(s)", size >> 10); > + } else if (size < (1ULL << 30)) { > + snprintf(buffer, sizeof(buffer), "%" PRIu64 " MB(s)", size >> 20); > + } else if (size < (1ULL << 40)) { > + snprintf(buffer, sizeof(buffer), "%" PRIu64 " GB(s)", size >> 30); > + } else { > + snprintf(buffer, sizeof(buffer), "%" PRIu64 " TB(s)", size >> 40); > + } > + > + return buffer; This returns a variable from the stack! Please make the target buffer caller defined. > +} > diff --git a/qemu-common.h b/qemu-common.h > index dfd3dc0..754b107 100644 > --- a/qemu-common.h > +++ b/qemu-common.h > @@ -137,6 +137,8 @@ time_t mktimegm(struct tm *tm); > int qemu_fls(int i); > int qemu_fdatasync(int fd); > int fcntl_setfl(int fd, int flag); > +int get_bits_from_size(size_t size); > +const char *bytes_to_str(uint64_t size); > > /* path.c */ > void init_paths(const char *prefix); > @@ -283,6 +285,7 @@ void qemu_iovec_destroy(QEMUIOVector *qiov); > void qemu_iovec_reset(QEMUIOVector *qiov); > void qemu_iovec_to_buffer(QEMUIOVector *qiov, void *buf); > void qemu_iovec_from_buffer(QEMUIOVector *qiov, const void *buf, size_t > count); > +void qemu_iovec_zero(QEMUIOVector *qiov); separate patch please. Alex
