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Re: [Qemu-devel] [PATCH 16/18] blockdev: Split up 'cache' option
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCH 16/18] blockdev: Split up 'cache' option |
Date: |
Fri, 26 Jul 2013 10:30:24 -0600 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130625 Thunderbird/17.0.7 |
On 07/23/2013 07:03 AM, Kevin Wolf wrote:
> The old 'cache' option really encodes three different boolean flags into
> a cache mode name, without providing all combinations. Make them three
> separate options instead and translate the old option to the new ones
> for drive_init().
>
> The specific boolean options take precedence if the old cache option is
> specified as well, so the following options are equivalent:
>
> -drive file=x,cache=none,cache.no-flush=true
> -drive file=x,cache.writeback=true,cache.direct=true,cache.no-flush=true
>
> Signed-off-by: Kevin Wolf <address@hidden>
> ---
> blockdev.c | 57 +++++++++++++++++++++++++++++++++++++++++++++++----------
> 1 file changed, 47 insertions(+), 10 deletions(-)
>
> +++ b/blockdev.c
> @@ -452,12 +452,15 @@ static DriveInfo *blockdev_init(QemuOpts *all_opts,
> }
> }
>
> - bdrv_flags |= BDRV_O_CACHE_WB;
> - if ((buf = qemu_opt_get(opts, "cache")) != NULL) {
> - if (bdrv_parse_cache_flags(buf, &bdrv_flags) != 0) {
The old code calls bdrv_parse_cache_flags() with non-zero bdrv_flags.
> @@ -751,6 +756,31 @@ DriveInfo *drive_init(QemuOpts *all_opts,
> BlockInterfaceType block_default_type)
>
> qemu_opt_rename(all_opts, "readonly", "read-only");
>
> + value = qemu_opt_get(all_opts, "cache");
> + if (value) {
> + int flags = 0;
> +
> + if (bdrv_parse_cache_flags(value, &flags) != 0) {
The new code calls it with flags starting at 0. But looking at
bdrv_parse_cache_flags(), the first thing that code did was zero out
BDRV_O_CACHE_MASK, which includes BDRV_O_CACHE_WB, so I think that in
reality you still end up with the same bits set at the end of that parse
call. Phew - that means you are actually getting rid of a dead |=
assignment. [And you proved that the block code is a twisty maze of
back-compat hacks.]
Reviewed-by: Eric Blake <address@hidden>
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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- Re: [Qemu-devel] [PATCH 13/18] blockdev: Rename I/O throttling options for QMP, (continued)
[Qemu-devel] [PATCH 12/18] QemuOpts: Add qemu_opt_unset(), Kevin Wolf, 2013/07/23
[Qemu-devel] [PATCH 15/18] blockdev: Rename 'readonly' option to 'read-only', Kevin Wolf, 2013/07/23
[Qemu-devel] [PATCH 14/18] qcow2: Use dashes instead of underscores in options, Kevin Wolf, 2013/07/23
[Qemu-devel] [PATCH 16/18] blockdev: Split up 'cache' option, Kevin Wolf, 2013/07/23
- Re: [Qemu-devel] [PATCH 16/18] blockdev: Split up 'cache' option,
Eric Blake <=
[Qemu-devel] [PATCH 17/18] Implement qdict_flatten(), Kevin Wolf, 2013/07/23
[Qemu-devel] [PATCH 18/18] blockdev: 'blockdev-add' QMP command, Kevin Wolf, 2013/07/23