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Re: [Qemu-devel] [Qemu-block] [PATCH v5 2/4] quorum: implement bdrv_add_
From: |
Max Reitz |
Subject: |
Re: [Qemu-devel] [Qemu-block] [PATCH v5 2/4] quorum: implement bdrv_add_child() and bdrv_del_child() |
Date: |
Wed, 7 Oct 2015 20:51:21 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 |
On 22.09.2015 09:44, Wen Congyang wrote:
> Signed-off-by: Wen Congyang <address@hidden>
> Signed-off-by: zhanghailiang <address@hidden>
> Signed-off-by: Gonglei <address@hidden>
> ---
> block.c | 6 ++---
> block/quorum.c | 72
> +++++++++++++++++++++++++++++++++++++++++++++++++--
> include/block/block.h | 3 +++
> 3 files changed, 76 insertions(+), 5 deletions(-)
>
> diff --git a/block.c b/block.c
> index 1b25e43..01f6d69 100644
> --- a/block.c
> +++ b/block.c
> @@ -1079,9 +1079,9 @@ static int bdrv_fill_options(QDict **options, const
> char **pfilename,
> return 0;
> }
>
> -static BdrvChild *bdrv_attach_child(BlockDriverState *parent_bs,
> - BlockDriverState *child_bs,
> - const BdrvChildRole *child_role)
> +BdrvChild *bdrv_attach_child(BlockDriverState *parent_bs,
> + BlockDriverState *child_bs,
> + const BdrvChildRole *child_role)
> {
> BdrvChild *child = g_new(BdrvChild, 1);
> *child = (BdrvChild) {
> diff --git a/block/quorum.c b/block/quorum.c
> index 8fe53b4..111a57b 100644
> --- a/block/quorum.c
> +++ b/block/quorum.c
> @@ -66,6 +66,9 @@ typedef struct QuorumVotes {
> typedef struct BDRVQuorumState {
> BlockDriverState **bs; /* children BlockDriverStates */
> int num_children; /* children count */
> + int max_children; /* The maximum children count, we need to
> reallocate
> + * bs if num_children grows larger than maximum.
> + */
> int threshold; /* if less than threshold children reads gave the
> * same result a quorum error occurs.
> */
> @@ -874,9 +877,9 @@ static int quorum_open(BlockDriverState *bs, QDict
> *options, int flags,
> ret = -EINVAL;
> goto exit;
> }
> - if (s->num_children < 2) {
> + if (s->num_children < 1) {
> error_setg(&local_err,
> - "Number of provided children must be greater than 1");
> + "Number of provided children must be 1 or more");
> ret = -EINVAL;
> goto exit;
> }
> @@ -925,6 +928,7 @@ static int quorum_open(BlockDriverState *bs, QDict
> *options, int flags,
> /* allocate the children BlockDriverState array */
> s->bs = g_new0(BlockDriverState *, s->num_children);
> opened = g_new0(bool, s->num_children);
> + s->max_children = s->num_children;
>
> for (i = 0; i < s->num_children; i++) {
> char indexstr[32];
> @@ -995,6 +999,67 @@ static void quorum_attach_aio_context(BlockDriverState
> *bs,
> }
> }
>
> +static void quorum_add_child(BlockDriverState *bs, BlockDriverState
> *child_bs,
> + Error **errp)
> +{
> + BDRVQuorumState *s = bs->opaque;
> +
> + bdrv_drain(bs);
> +
> + if (s->num_children == s->max_children) {
> + if (s->max_children >= INT_MAX) {
Opposing Berto (:-)), I like >= even if the > part is actually
impossible. I myself like to use constructs such as:
for (i = 0; i < n; i++) {
/* ... */
}
if (i >= n) {
/* ... */
}
Even though @i can never exceed @n after the loop. This is because my
way of thinking is "What if it could exceed @n? Then I'd like to take
this branch as well." The same applies here. s->max_children can never
exceed INT_MAX, but if it could, we'd want that to be an error, too.
I do find myself in discussions about that from time to time, especially
since others prefer (for the example above):
for (i = 0; i < n; i++) { /* ... */ }
assert(i <= n);
if (i == n) { /* ... */ }
Or the like.
> + error_setg(errp, "Too many children");
> + return;
> + }
> +
> + s->bs = g_renew(BlockDriverState *, s->bs, s->max_children + 1);
> + s->bs[s->num_children] = NULL;
> + s->max_children++;
> + }
Just a suggestion, please feel free to ignore it completely:
You can drop the s->max_children field and just always call g_renew()
with s->num_children + 1 as the @count parameter. There shouldn't be any
(visible) performance penalty, but it would simplify the code.
> +
> + bdrv_ref(child_bs);
> + bdrv_attach_child(bs, child_bs, &child_format);
> + s->bs[s->num_children++] = child_bs;
> +}
> +
> +static void quorum_del_child(BlockDriverState *bs, BlockDriverState
> *child_bs,
> + Error **errp)
> +{
> + BDRVQuorumState *s = bs->opaque;
> + BdrvChild *child;
> + int i;
> +
> + for (i = 0; i < s->num_children; i++) {
> + if (s->bs[i] == child_bs) {
> + break;
> + }
> + }
> +
> + QLIST_FOREACH(child, &bs->children, next) {
> + if (child->bs == child_bs) {
> + break;
> + }
> + }
> +
> + /* we have checked it in bdrv_del_child() */
> + assert(i < s->num_children && child);
> +
> + if (s->num_children <= s->threshold) {
> + error_setg(errp,
> + "The number of children cannot be lower than the vote threshold
> %d",
> + s->threshold);
> + return;
> + }
> +
> + bdrv_drain(bs);
> + /* We can safely remove this child now */
> + memmove(&s->bs[i], &s->bs[i + 1],
> + (s->num_children - i - 1) * sizeof(void *));
I'd use a matching type here, i.e. sizeof(BlockDriverState *) before
Kevin's bdrv_swap() series or sizeof(BdrvChild *) afterwards.
> + s->num_children--;
> + s->bs[s->num_children] = NULL;
In case you do decide to drop s->max_children, you could replace this by
a call to g_renew on s->bs (or s->children).
In any case, as Berto said, this line is unnecessary.
Max
> + bdrv_unref_child(bs, child);
> +}
> +
> static void quorum_refresh_filename(BlockDriverState *bs)
> {
> BDRVQuorumState *s = bs->opaque;
> @@ -1049,6 +1114,9 @@ static BlockDriver bdrv_quorum = {
> .bdrv_detach_aio_context = quorum_detach_aio_context,
> .bdrv_attach_aio_context = quorum_attach_aio_context,
>
> + .bdrv_add_child = quorum_add_child,
> + .bdrv_del_child = quorum_del_child,
> +
> .is_filter = true,
> .bdrv_recurse_is_first_non_filter = quorum_recurse_is_first_non_filter,
> };
> diff --git a/include/block/block.h b/include/block/block.h
> index 665c56f..bd97399 100644
> --- a/include/block/block.h
> +++ b/include/block/block.h
> @@ -514,6 +514,9 @@ void bdrv_disable_copy_on_read(BlockDriverState *bs);
> void bdrv_ref(BlockDriverState *bs);
> void bdrv_unref(BlockDriverState *bs);
> void bdrv_unref_child(BlockDriverState *parent, BdrvChild *child);
> +BdrvChild *bdrv_attach_child(BlockDriverState *parent_bs,
> + BlockDriverState *child_bs,
> + const BdrvChildRole *child_role);
>
> bool bdrv_op_is_blocked(BlockDriverState *bs, BlockOpType op, Error **errp);
> void bdrv_op_block(BlockDriverState *bs, BlockOpType op, Error *reason);
>
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- Re: [Qemu-devel] [Qemu-block] [PATCH v5 2/4] quorum: implement bdrv_add_child() and bdrv_del_child(),
Max Reitz <=