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Re: [Qemu-devel] [PATCH v3 1/2] block/quorum: add simple read pattern su
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCH v3 1/2] block/quorum: add simple read pattern support |
Date: |
Tue, 15 Jul 2014 06:14:32 -0600 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 |
On 07/15/2014 12:34 AM, Liu Yuan wrote:
> This patch adds single read pattern to quorum driver and quorum vote is
> default
> pattern.
>
> For now we do a quorum vote on all the reads, it is designed for unreliable
> underlying storage such as non-redundant NFS to make sure data integrity at
> the
> cost of the read performance.
>
> */
> +
> +#define READ_PATTERN_QUORUM 0 /* default */
> +#define READ_PATTERN_FIFO 1
> + int read_pattern; /* fifo: read a single child and try first one
> + * first. If error, try next child in an
> + * FIFO order specifed by command line.
> + * Return error if no child read succeeds.
> + * quorum: read all the children and do a quorum
> + * vote on reads.
> + */
Please swap the order of your two patches, or squash them back into one.
If you define the qapi enum first, then you don't need to open-code
these #defines; instead, the qapi code will generate a typedef that puts
the C enum QuorumReadPattern into play, so that this declaration becomes
'QuorumReadPattern read_pattern;'...
> @@ -263,6 +292,21 @@ static void quorum_aio_cb(void *opaque, int ret)
> BDRVQuorumState *s = acb->common.bs->opaque;
> bool rewrite = false;
>
> + if (acb->is_read && s->read_pattern == READ_PATTERN_FIFO) {
...and code like this can compare against the constant
QUORUM_READ_PATTERN_FIFO (which will be generated for you from the .json
file)...
> + read_pattern = qemu_opt_get(opts, QUORUM_OPT_READ_PATTERN);
> + if (read_pattern) {
> + if (strcmp(read_pattern, "fifo") == 0) {
> + s->read_pattern = READ_PATTERN_FIFO;
> + } else if (strcmp(read_pattern, "quorum") == 0) {
> + s->read_pattern = READ_PATTERN_QUORUM;
> + } else {
> + error_setg(&local_err,
> + "Please set read-pattern as fifo or quorum\n");
> + ret = -EINVAL;
> + goto exit;
> + }
...and instead of open-coding this, you should use parse_enum_option().
Also, by using the generated list here, if you later add a third read
pattern, then this parser code doesn't have to change, but already
automatically covers all valid options encoded in the qapi list.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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