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From: Eric Blake <eblake@redhat.com>
To: libguestfs@redhat.com
Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, nbd@other.debian.org
Subject: Re: [Qemu-devel] [Libguestfs] [nbdkit PATCH 3/3] plugins: Add .can_fast_zero hook
Date: Fri, 23 Aug 2019 16:16:18 -0500
Message-ID: <0f743b37-6308-24d0-eae0-5f939af9dae2@redhat.com> (raw)
In-Reply-To: <20190823144054.27420-4-eblake@redhat.com>

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On 8/23/19 9:40 AM, Eric Blake wrote:
> Allow plugins to affect the handling of the new NBD_CMD_FLAG_FAST_ZERO
> flag, then update affected plugins.  In particular, in-memory plugins
> are always fast; the full plugin is better served by omitting .zero
> and relying on .pwrite fallback; nbd takes advantage of libnbd
> extensions proposed in parallel to pass through support; and
> v2 language bindings expose the choice to their scripts.
> 

> +++ b/server/plugins.c
> @@ -404,11 +404,25 @@ plugin_can_zero (struct backend *b, struct connection *conn)
>  static int
>  plugin_can_fast_zero (struct backend *b, struct connection *conn)
>  {
> +  struct backend_plugin *p = container_of (b, struct backend_plugin, backend);
> +  int r;
> +
>    assert (connection_get_handle (conn, 0));
> 
>    debug ("can_fast_zero");
> 
> -  return 0; /* Upcoming patch will actually add support. */
> +  if (p->plugin.can_fast_zero)
> +    return p->plugin.can_fast_zero (connection_get_handle (conn, 0));
> +  /* Advertise support for fast zeroes if no .zero or .can_zero is
> +   * false: in those cases, we fail fast instead of using .pwrite.
> +   * This also works when v1 plugin has only ._zero_old.
> +   */
> +  if (p->plugin.zero == NULL)
> +    return 1;
> +  r = plugin_can_zero (b, conn);
> +  if (r == -1)
> +    return -1;
> +  return !r;
>  }
> 

Needs this squashed in for libnbd to pass rather than skip its new
'can-fast-zero-flag' test:


diff --git i/server/plugins.c w/server/plugins.c
index 84329cf4..695a77ab 100644
--- i/server/plugins.c
+++ w/server/plugins.c
@@ -208,6 +208,7 @@ plugin_dump_fields (struct backend *b)
   HAS (can_cache);
   HAS (cache);
   HAS (thread_model);
+  HAS (can_fast_zero);
 #undef HAS

   /* Custom fields. */


-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org


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  reply index

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-23 14:30 [Qemu-devel] cross-project patches: Add NBD Fast Zero support Eric Blake
2019-08-23 14:34 ` [Qemu-devel] [PATCH 0/1] NBD protocol change to add fast zero support Eric Blake
2019-08-23 14:34   ` [Qemu-devel] [PATCH 1/1] protocol: Add NBD_CMD_FLAG_FAST_ZERO Eric Blake
2019-08-23 18:48     ` Wouter Verhelst
2019-08-23 18:58       ` Eric Blake
2019-08-24  6:44         ` Wouter Verhelst
2019-08-28  9:57     ` Vladimir Sementsov-Ogievskiy
2019-08-28 13:04       ` Eric Blake
2019-08-28 13:45         ` Vladimir Sementsov-Ogievskiy
2019-09-03 20:53   ` [Qemu-devel] [Libguestfs] [PATCH 0/1] NBD protocol change to add fast zero support Eric Blake
2019-08-23 14:37 ` [Qemu-devel] [PATCH 0/5] Add NBD fast zero support to qemu client and server Eric Blake
2019-08-23 14:37   ` [Qemu-devel] [PATCH 1/5] nbd: Improve per-export flag handling in server Eric Blake
2019-08-30 18:00     ` Vladimir Sementsov-Ogievskiy
2019-08-30 23:10       ` Eric Blake
2019-08-30 23:32         ` Eric Blake
2019-09-03 16:39           ` Eric Blake
2019-09-04 17:08     ` Vladimir Sementsov-Ogievskiy
2019-08-23 14:37   ` [Qemu-devel] [PATCH 2/5] nbd: Prepare for NBD_CMD_FLAG_FAST_ZERO Eric Blake
2019-08-30 18:07     ` Vladimir Sementsov-Ogievskiy
2019-08-30 23:37       ` Eric Blake
2019-08-31  8:11         ` Vladimir Sementsov-Ogievskiy
2019-09-03 18:49       ` Eric Blake
2019-08-31  8:20     ` Vladimir Sementsov-Ogievskiy
2019-08-23 14:37   ` [Qemu-devel] [PATCH 3/5] nbd: Implement client use of NBD FAST_ZERO Eric Blake
2019-08-30 18:11     ` Vladimir Sementsov-Ogievskiy
2019-08-23 14:37   ` [Qemu-devel] [PATCH 4/5] nbd: Implement server " Eric Blake
2019-08-30 18:40     ` Vladimir Sementsov-Ogievskiy
2019-08-23 14:37   ` [Qemu-devel] [PATCH 5/5] nbd: Tolerate more errors to structured reply request Eric Blake
2019-08-23 16:41     ` Eric Blake
2019-08-28 13:55   ` [Qemu-devel] [PATCH 0/5] Add NBD fast zero support to qemu client and server Vladimir Sementsov-Ogievskiy
2019-08-28 14:05     ` Eric Blake
2019-08-23 14:38 ` [Qemu-devel] [libnbd PATCH 0/1] libnbd support for new fast zero Eric Blake
2019-08-23 14:38   ` [Qemu-devel] [libnbd PATCH 1/1] api: Add support for FAST_ZERO flag Eric Blake
2019-08-27 12:25     ` [Qemu-devel] [Libguestfs] " Richard W.M. Jones
2019-08-23 14:40 ` [Qemu-devel] [nbdkit PATCH 0/3] nbdkit support for new NBD fast zero Eric Blake
2019-08-23 14:40   ` [Qemu-devel] [nbdkit PATCH 1/3] server: Add internal support for NBDKIT_FLAG_FAST_ZERO Eric Blake
2019-08-23 14:40   ` [Qemu-devel] [nbdkit PATCH 2/3] filters: Add .can_fast_zero hook Eric Blake
2019-08-23 14:40   ` [Qemu-devel] [nbdkit PATCH 3/3] plugins: " Eric Blake
2019-08-23 21:16     ` Eric Blake [this message]
2019-08-27 15:43     ` [Qemu-devel] [Libguestfs] " Richard W.M. Jones
2019-08-23 15:05 ` [Qemu-devel] cross-project patches: Add NBD Fast Zero support Vladimir Sementsov-Ogievskiy
2019-08-27 12:14 ` [Qemu-devel] [Libguestfs] " Richard W.M. Jones
2019-08-27 13:23   ` Eric Blake

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