[Qemu-devel] [PATCH v2 1/1] nbd: add zero-init parameter

["Denis V. Lunev" <den@openvz.org>]

When using a nbd block device, the info about necessity of prior disk
zeroing could significantly improve the speed of certain operations
(e.g. backups).

This patch also will allow to preserve QCOW2 images during migration.
Management software now may specify zero-init option and thus abscent
areas in the original QCOW2 image will not be marked as zeroes in the
target image. This is tight distiction but it is here.

Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: Paolo Bonzini <pbonzini@redhat.com>
CC: Kevin Wolf <kwolf@redhat.com>
CC: Max Reitz <mreitz@redhat.com>
---
 block/nbd.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/block/nbd.c b/block/nbd.c
index 6bc06d6..eed06d1 100644
--- a/block/nbd.c
+++ b/block/nbd.c
@@ -45,6 +45,7 @@ typedef struct BDRVNBDState {
 
     /* For nbd_refresh_filename() */
     char *path, *host, *port, *export, *tlscredsid;
+    bool zero_init;
 } BDRVNBDState;
 
 static int nbd_parse_uri(const char *filename, QDict *options)
@@ -194,6 +195,7 @@ out:
 static SocketAddress *nbd_config(BDRVNBDState *s, QemuOpts *opts, Error **errp)
 {
     SocketAddress *saddr;
+    const char *zero_init;
 
     s->path = g_strdup(qemu_opt_get(opts, "path"));
     s->host = g_strdup(qemu_opt_get(opts, "host"));
@@ -232,6 +234,11 @@ static SocketAddress *nbd_config(BDRVNBDState *s, QemuOpts *opts, Error **errp)
 
     s->export = g_strdup(qemu_opt_get(opts, "export"));
 
+    zero_init = qemu_opt_get(opts, "zero-init");
+    if (zero_init != NULL) {
+        s->zero_init = strcmp(zero_init, "on") == 0;
+    }
+
     return saddr;
 }
 
@@ -322,6 +329,11 @@ static QemuOptsList nbd_runtime_opts = {
             .type = QEMU_OPT_STRING,
             .help = "ID of the TLS credentials to use",
         },
+        {
+            .name = "zero-init",
+            .type = QEMU_OPT_BOOL,
+            .help = "Zero-initialized image flag",
+        },
     },
 };
 
@@ -483,6 +495,12 @@ static void nbd_refresh_filename(BlockDriverState *bs, QDict *options)
     bs->full_open_options = opts;
 }
 
+static int nbd_has_zero_init(BlockDriverState *bs)
+{
+    BDRVNBDState *s = bs->opaque;
+    return s->zero_init;
+}
+
 static BlockDriver bdrv_nbd = {
     .format_name                = "nbd",
     .protocol_name              = "nbd",
@@ -499,6 +517,7 @@ static BlockDriver bdrv_nbd = {
     .bdrv_detach_aio_context    = nbd_detach_aio_context,
     .bdrv_attach_aio_context    = nbd_attach_aio_context,
     .bdrv_refresh_filename      = nbd_refresh_filename,
+    .bdrv_has_zero_init         = nbd_has_zero_init,
 };
 
 static BlockDriver bdrv_nbd_tcp = {
@@ -517,6 +536,7 @@ static BlockDriver bdrv_nbd_tcp = {
     .bdrv_detach_aio_context    = nbd_detach_aio_context,
     .bdrv_attach_aio_context    = nbd_attach_aio_context,
     .bdrv_refresh_filename      = nbd_refresh_filename,
+    .bdrv_has_zero_init         = nbd_has_zero_init,
 };
 
 static BlockDriver bdrv_nbd_unix = {
@@ -535,6 +555,7 @@ static BlockDriver bdrv_nbd_unix = {
     .bdrv_detach_aio_context    = nbd_detach_aio_context,
     .bdrv_attach_aio_context    = nbd_attach_aio_context,
     .bdrv_refresh_filename      = nbd_refresh_filename,
+    .bdrv_has_zero_init         = nbd_has_zero_init,
 };
 
 static void bdrv_nbd_init(void)
-- 
2.5.0