From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=33222 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PiVvX-0004Gp-Fm for qemu-devel@nongnu.org; Thu, 27 Jan 2011 12:46:36 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1PiVvW-00066J-6s for qemu-devel@nongnu.org; Thu, 27 Jan 2011 12:46:35 -0500 Received: from mail-vw0-f45.google.com ([209.85.212.45]:36462) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1PiVvW-00066D-2F for qemu-devel@nongnu.org; Thu, 27 Jan 2011 12:46:34 -0500 Received: by vws12 with SMTP id 12so871975vws.4 for ; Thu, 27 Jan 2011 09:46:33 -0800 (PST) Message-ID: <4D41AF53.8070701@codemonkey.ws> Date: Thu, 27 Jan 2011 11:45:55 -0600 From: Anthony Liguori MIME-Version: 1.0 Subject: Re: [Qemu-devel] [PATCH] qcow2: Add full image preallocation option References: <1296143534-13495-1-git-send-email-kwolf@redhat.com> In-Reply-To: <1296143534-13495-1-git-send-email-kwolf@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: qemu-devel@nongnu.org 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 > --- > 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 } > }; >