[Qemu-devel] [PATCH v3] block/rbd: add preallocation support

[Stefano Garzarella]

This patch adds the support of preallocation (off/full) for the RBD
block driver.
If rbd_writesame() is available and supports zeroed buffers, we use
it to quickly fill the image when full preallocation is required.

Signed-off-by: Stefano Garzarella <address@hidden>
---
v3:
 - rebased on master
 - filled with zeroed buffer [Max]
 - used rbd_writesame() only when we can disable the discard of zeroed
   buffers
 - added 'since: 4.2' in qapi/block-core.json [Max]
 - used buffer as large as the "stripe unit"
---
 block/rbd.c          | 202 ++++++++++++++++++++++++++++++++++++++++---
 qapi/block-core.json |   5 +-
 2 files changed, 192 insertions(+), 15 deletions(-)

diff --git a/block/rbd.c b/block/rbd.c
index 59757b3120..d923a5a26c 100644
--- a/block/rbd.c
+++ b/block/rbd.c
@@ -64,6 +64,7 @@
 #define OBJ_MAX_SIZE (1UL << OBJ_DEFAULT_OBJ_ORDER)
 
 #define RBD_MAX_SNAPS 100
+#define RBD_DEFAULT_CONCURRENT_OPS 10
 
 /* The LIBRBD_SUPPORTS_IOVEC is defined in librbd.h */
 #ifdef LIBRBD_SUPPORTS_IOVEC
@@ -104,6 +105,7 @@ typedef struct BDRVRBDState {
     char *image_name;
     char *snap;
     uint64_t image_size;
+    bool ws_zero_supported; /* rbd_writesame() supports zeroed buffers */
 } BDRVRBDState;
 
 static int qemu_rbd_connect(rados_t *cluster, rados_ioctx_t *io_ctx,
@@ -333,6 +335,155 @@ static void qemu_rbd_memset(RADOSCB *rcb, int64_t offs)
     }
 }
 
+static int qemu_rbd_get_max_concurrent_ops(rados_t cluster)
+{
+    char buf[16];
+    int ret, max_concurrent_ops;
+
+    ret = rados_conf_get(cluster, "rbd_concurrent_management_ops", buf,
+                         sizeof(buf));
+    if (ret < 0) {
+        return RBD_DEFAULT_CONCURRENT_OPS;
+    }
+
+    ret = qemu_strtoi(buf, NULL, 10, &max_concurrent_ops);
+    if (ret < 0) {
+        return RBD_DEFAULT_CONCURRENT_OPS;
+    }
+
+    return max_concurrent_ops;
+}
+
+static int qemu_rbd_do_truncate(rados_t cluster, rbd_image_t image,
+                                int64_t offset, PreallocMode prealloc,
+                                bool ws_zero_supported, Error **errp)
+{
+    uint64_t current_length;
+    char *buf = NULL;
+    int ret;
+
+    ret = rbd_get_size(image, &current_length);
+    if (ret < 0) {
+        error_setg_errno(errp, -ret, "Failed to get file length");
+        goto out;
+    }
+
+    if (current_length > offset && prealloc != PREALLOC_MODE_OFF) {
+        error_setg(errp, "Cannot use preallocation for shrinking files");
+        ret = -ENOTSUP;
+        goto out;
+    }
+
+    switch (prealloc) {
+    case PREALLOC_MODE_FULL: {
+        uint64_t buf_size, current_offset = current_length;
+        ssize_t bytes;
+
+        ret = rbd_get_stripe_unit(image, &buf_size);
+        if (ret < 0) {
+            error_setg_errno(errp, -ret, "Failed to get stripe unit");
+            goto out;
+        }
+
+        ret = rbd_resize(image, offset);
+        if (ret < 0) {
+            error_setg_errno(errp, -ret, "Failed to resize file");
+            goto out;
+        }
+
+        buf = g_malloc0(buf_size);
+
+#ifdef LIBRBD_SUPPORTS_WRITESAME
+        if (ws_zero_supported) {
+            uint64_t writesame_max_size;
+            int max_concurrent_ops;
+
+            max_concurrent_ops = qemu_rbd_get_max_concurrent_ops(cluster);
+            /*
+             * We limit the rbd_writesame() size to avoid to spawn more then
+             * 'rbd_concurrent_management_ops' concurrent operations.
+             */
+            writesame_max_size = MIN(buf_size * max_concurrent_ops, INT_MAX);
+
+            while (offset - current_offset > buf_size) {
+                bytes = MIN(offset - current_offset, writesame_max_size);
+                /*
+                 * rbd_writesame() supports only request where the size of the
+                 * operation is multiple of buffer size.
+                 */
+                bytes -= bytes % buf_size;
+
+                bytes = rbd_writesame(image, current_offset, bytes, buf,
+                                      buf_size, 0);
+                if (bytes < 0) {
+                    ret = bytes;
+                    error_setg_errno(errp, -ret,
+                                     "Failed to write for preallocation");
+                    goto out;
+                }
+
+                current_offset += bytes;
+            }
+        }
+#endif /* LIBRBD_SUPPORTS_WRITESAME */
+
+        while (current_offset < offset) {
+            bytes = rbd_write(image, current_offset,
+                              MIN(offset - current_offset, buf_size), buf);
+            if (bytes < 0) {
+                ret = bytes;
+                error_setg_errno(errp, -ret,
+                                 "Failed to write for preallocation");
+                goto out;
+            }
+
+            current_offset += bytes;
+        }
+
+        ret = rbd_flush(image);
+        if (ret < 0) {
+            error_setg_errno(errp, -ret, "Failed to flush the file");
+            goto out;
+        }
+
+        break;
+    }
+    case PREALLOC_MODE_OFF:
+        ret = rbd_resize(image, offset);
+        if (ret < 0) {
+            error_setg_errno(errp, -ret, "Failed to resize file");
+            goto out;
+        }
+        break;
+    default:
+        error_setg(errp, "Unsupported preallocation mode: %s",
+                   PreallocMode_str(prealloc));
+        ret = -ENOTSUP;
+        goto out;
+    }
+
+    ret = 0;
+
+out:
+    g_free(buf);
+    return ret;
+}
+
+static bool qemu_rbd_writesame_zero_supported(rados_t *cluster)
+{
+    int ret = 1;
+
+#ifdef LIBRBD_SUPPORTS_WRITESAME
+    /*
+     * When "rbd_discard_on_zeroed_write_same" is not available, 
rbd_writesame()
+     * can discard requests with zeroed buffer.
+     */
+    ret = rados_conf_set(*cluster, "rbd_discard_on_zeroed_write_same", 
"false");
+#endif
+
+    return ret == 0;
+}
+
 static QemuOptsList runtime_opts = {
     .name = "rbd",
     .head = QTAILQ_HEAD_INITIALIZER(runtime_opts.head),
@@ -378,6 +529,7 @@ static int qemu_rbd_do_create(BlockdevCreateOptions 
*options,
     BlockdevCreateOptionsRbd *opts = &options->u.rbd;
     rados_t cluster;
     rados_ioctx_t io_ctx;
+    rbd_image_t image;
     int obj_order = 0;
     int ret;
 
@@ -406,13 +558,23 @@ static int qemu_rbd_do_create(BlockdevCreateOptions 
*options,
         return ret;
     }
 
-    ret = rbd_create(io_ctx, opts->location->image, opts->size, &obj_order);
+    ret = rbd_create(io_ctx, opts->location->image, 0, &obj_order);
     if (ret < 0) {
         error_setg_errno(errp, -ret, "error rbd create");
         goto out;
     }
 
-    ret = 0;
+    ret = rbd_open(io_ctx, opts->location->image, &image, NULL);
+    if (ret < 0) {
+        error_setg_errno(errp, -ret, "error rbd open");
+        goto out;
+    }
+
+    ret = qemu_rbd_do_truncate(cluster, image, opts->size, opts->preallocation,
+                               qemu_rbd_writesame_zero_supported(&cluster),
+                               errp);
+
+    rbd_close(image);
 out:
     rados_ioctx_destroy(io_ctx);
     rados_shutdown(cluster);
@@ -433,6 +595,7 @@ static int coroutine_fn qemu_rbd_co_create_opts(const char 
*filename,
     BlockdevOptionsRbd *loc;
     Error *local_err = NULL;
     const char *keypairs, *password_secret;
+    char *prealloc;
     QDict *options = NULL;
     int ret = 0;
 
@@ -451,6 +614,16 @@ static int coroutine_fn qemu_rbd_co_create_opts(const char 
*filename,
                                                    BLOCK_OPT_CLUSTER_SIZE, 0);
     rbd_opts->has_cluster_size = (rbd_opts->cluster_size != 0);
 
+    prealloc = qemu_opt_get_del(opts, BLOCK_OPT_PREALLOC);
+    rbd_opts->preallocation = qapi_enum_parse(&PreallocMode_lookup, prealloc,
+                                              PREALLOC_MODE_OFF, &local_err);
+    g_free(prealloc);
+    if (local_err) {
+        ret = -EINVAL;
+        error_propagate(errp, local_err);
+        goto exit;
+    }
+
     options = qdict_new();
     qemu_rbd_parse_filename(filename, options, &local_err);
     if (local_err) {
@@ -770,6 +943,7 @@ static int qemu_rbd_open(BlockDriverState *bs, QDict 
*options, int flags,
 
     s->snap = g_strdup(opts->snapshot);
     s->image_name = g_strdup(opts->image);
+    s->ws_zero_supported = qemu_rbd_writesame_zero_supported(&s->cluster);
 
     /* rbd_open is always r/w */
     r = rbd_open(s->io_ctx, s->image_name, &s->image, s->snap);
@@ -1089,21 +1263,16 @@ static int coroutine_fn 
qemu_rbd_co_truncate(BlockDriverState *bs,
                                              PreallocMode prealloc,
                                              Error **errp)
 {
-    int r;
-
-    if (prealloc != PREALLOC_MODE_OFF) {
-        error_setg(errp, "Unsupported preallocation mode '%s'",
-                   PreallocMode_str(prealloc));
-        return -ENOTSUP;
-    }
+    BDRVRBDState *s = bs->opaque;
+    int ret;
 
-    r = qemu_rbd_resize(bs, offset);
-    if (r < 0) {
-        error_setg_errno(errp, -r, "Failed to resize file");
-        return r;
+    ret = qemu_rbd_do_truncate(s->cluster, s->image, offset, prealloc,
+                               s->ws_zero_supported, errp);
+    if (ret == 0) {
+        s->image_size = offset;
     }
 
-    return 0;
+    return ret;
 }
 
 static int qemu_rbd_snap_create(BlockDriverState *bs,
@@ -1256,6 +1425,11 @@ static QemuOptsList qemu_rbd_create_opts = {
             .type = QEMU_OPT_SIZE,
             .help = "RBD object size"
         },
+        {
+            .name = BLOCK_OPT_PREALLOC,
+            .type = QEMU_OPT_STRING,
+            .help = "Preallocation mode (allowed values: off, full)"
+        },
         {
             .name = "password-secret",
             .type = QEMU_OPT_STRING,
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 0d43d4f37c..ff55171f8d 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -4346,13 +4346,16 @@
 #                   point to a snapshot.
 # @size             Size of the virtual disk in bytes
 # @cluster-size     RBD object size
+# @preallocation    Preallocation mode for the new image (since: 4.2)
+#                   (default: off; allowed values: off, full)
 #
 # Since: 2.12
 ##
 { 'struct': 'BlockdevCreateOptionsRbd',
   'data': { 'location':         'BlockdevOptionsRbd',
             'size':             'size',
-            '*cluster-size' :   'size' } }
+            '*cluster-size' :   'size',
+            '*preallocation':   'PreallocMode' } }
 
 ##
 # @BlockdevVmdkSubformat:
-- 
2.20.1