On 01/27/2011 09:52 AM, Kevin Wolf wrote:
This adds a preallocation=full mode to qcow2 image creation, which does not only allocate metadata for the whole image, but also writes zeros to it, creating a non-sparse image file.
The writing zeros bit is in order to support physical devices? Would it be better to have a flag in BlockDriverState that indicated whether uninitialized sectors could be assumed to be zero filled and key off of that?
Regards, Anthony Liguori
Signed-off-by: Kevin Wolf<kw...@redhat.com> --- block/qcow2.c | 45 ++++++++++++++++++++++++++++++++++++++++----- 1 files changed, 40 insertions(+), 5 deletions(-) diff --git a/block/qcow2.c b/block/qcow2.c index a1773e4..90cf2ca 100644 --- a/block/qcow2.c +++ b/block/qcow2.c @@ -838,7 +838,15 @@ static int qcow2_change_backing_file(BlockDriverState *bs, return qcow2_update_ext_header(bs, backing_file, backing_fmt); } -static int preallocate(BlockDriverState *bs) +enum prealloc_mode { + PREALLOC_OFF = 0, + PREALLOC_METADATA, + PREALLOC_FULL, +}; + +#define IO_BUF_SIZE (2 * 1024 * 1024) + +static int preallocate(BlockDriverState *bs, enum prealloc_mode mode) { uint64_t nb_sectors; uint64_t offset; @@ -846,11 +854,14 @@ static int preallocate(BlockDriverState *bs) int ret; QCowL2Meta meta; + assert(mode != PREALLOC_OFF); + nb_sectors = bdrv_getlength(bs)>> 9; offset = 0; QLIST_INIT(&meta.dependent_requests); meta.cluster_offset = 0; + /* First allocate metadata in _really_ big chunks */ while (nb_sectors) { num = MIN(nb_sectors, INT_MAX>> 9); ret = qcow2_alloc_cluster_offset(bs, offset, 0, num,&num,&meta); @@ -874,6 +885,28 @@ static int preallocate(BlockDriverState *bs) offset += num<< 9; } + /* Then write zeros to the cluster data, if requested */ + if (mode == PREALLOC_FULL) { + void *buf = qemu_mallocz(IO_BUF_SIZE); + + nb_sectors = bdrv_getlength(bs)>> BDRV_SECTOR_BITS; + offset = 0; + + while (nb_sectors) { + num = MIN(nb_sectors, IO_BUF_SIZE / BDRV_SECTOR_SIZE); + ret = bdrv_write(bs, offset>> BDRV_SECTOR_BITS, buf, num); + if (ret< 0) { + qemu_free(buf); + return ret; + } + + nb_sectors -= num; + offset += num<< 9; + } + + qemu_free(buf); + } + /* * It is expected that the image file is large enough to actually contain * all of the allocated clusters (otherwise we get failing reads after @@ -1006,7 +1039,7 @@ static int qcow2_create2(const char *filename, int64_t total_size, /* And if we're supposed to preallocate metadata, do that now */ if (prealloc) { - ret = preallocate(bs); + ret = preallocate(bs, prealloc); if (ret< 0) { goto out; } @@ -1043,9 +1076,11 @@ static int qcow2_create(const char *filename, QEMUOptionParameter *options) } } else if (!strcmp(options->name, BLOCK_OPT_PREALLOC)) { if (!options->value.s || !strcmp(options->value.s, "off")) { - prealloc = 0; + prealloc = PREALLOC_OFF; } else if (!strcmp(options->value.s, "metadata")) { - prealloc = 1; + prealloc = PREALLOC_METADATA; + } else if (!strcmp(options->value.s, "full")) { + prealloc = PREALLOC_FULL; } else { fprintf(stderr, "Invalid preallocation mode: '%s'\n", options->value.s); @@ -1336,7 +1371,7 @@ static QEMUOptionParameter qcow2_create_options[] = { { .name = BLOCK_OPT_PREALLOC, .type = OPT_STRING, - .help = "Preallocation mode (allowed values: off, metadata)" + .help = "Preallocation mode (allowed values: off, metadata, full)" }, { NULL } };