Il 15/05/2013 16:34, Stefan Hajnoczi ha scritto:
> The bdrv_add_before_write_cb() function installs a callback that is
> invoked before a write request is processed. This will be used to
> implement copy-on-write point-in-time snapshots where we need to copy
> out old data before overwriting it.
Perhaps a notifier list that receives the BdrvTrackedRequest? (BTW we
should probably remove all the notifier_remove wrappers, they're useless).
The BdrvTrackedRequest pointer would also act as a unique id of the request.
> Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
> ---
> block.c | 37 +++++++++++++++++++++++++++++++++++++
> include/block/block_int.h | 32 ++++++++++++++++++++++++++++++++
> 2 files changed, 69 insertions(+)
>
> diff --git a/block.c b/block.c
> index 3f87489..0fd7167 100644
> --- a/block.c
> +++ b/block.c
> @@ -308,6 +308,7 @@ BlockDriverState *bdrv_new(const char *device_name)
> }
> bdrv_iostatus_disable(bs);
> notifier_list_init(&bs->close_notifiers);
> + QTAILQ_INIT(&bs->before_write_cbs);
>
> return bs;
> }
> @@ -1383,6 +1384,8 @@ void bdrv_close(BlockDriverState *bs)
> bs->growable = 0;
> QDECREF(bs->options);
> bs->options = NULL;
> + assert(QTAILQ_EMPTY(&bs->before_write_cbs));
> + QTAILQ_INIT(&bs->before_write_cbs);
INIT not needed if you assert before.
Paolo
>
> if (bs->file != NULL) {
> bdrv_delete(bs->file);
> @@ -2587,6 +2590,22 @@ static int coroutine_fn
> bdrv_co_do_write_zeroes(BlockDriverState *bs,
> return ret;
> }
>
> +struct BDRVBeforeWrite {
> + BDRVBeforeWriteFunc *cb;
> + QTAILQ_ENTRY(BDRVBeforeWrite) list;
> +};
> +
> +static void invoke_before_write_cb(BlockDriverState *bs, int64_t sector_num,
> + int nb_sectors, QEMUIOVector *qiov)
> +{
> + BDRVBeforeWrite *before_write;
> + BDRVBeforeWrite *tmp;
> + QTAILQ_FOREACH_SAFE(before_write, &bs->before_write_cbs, list, tmp) {
> + before_write->cb(bs, sector_num, nb_sectors, qiov);
> + }
> +}
> +
> +
> /*
> * Handle a write request in coroutine context
> */
> @@ -2619,6 +2638,8 @@ static int coroutine_fn
> bdrv_co_do_writev(BlockDriverState *bs,
>
> tracked_request_begin(&req, bs, sector_num, nb_sectors, true);
>
> + invoke_before_write_cb(bs, sector_num, nb_sectors, qiov);
> +
> if (flags & BDRV_REQ_ZERO_WRITE) {
> ret = bdrv_co_do_write_zeroes(bs, sector_num, nb_sectors);
> } else {
> @@ -4883,3 +4904,19 @@ AioContext *bdrv_get_aio_context(BlockDriverState *bs)
> /* Currently BlockDriverState always uses the main loop AioContext */
> return qemu_get_aio_context();
> }
> +
> +BDRVBeforeWrite *bdrv_add_before_write_cb(BlockDriverState *bs,
> + BDRVBeforeWriteFunc *cb)
> +{
> + BDRVBeforeWrite *elem = g_slice_new(BDRVBeforeWrite);
> + elem->cb = cb;
> + QTAILQ_INSERT_TAIL(&bs->before_write_cbs, elem, list);
> + return elem;
> +}
> +
> +void bdrv_remove_before_write_cb(BlockDriverState *bs,
> + BDRVBeforeWrite *before_write)
> +{
> + QTAILQ_REMOVE(&bs->before_write_cbs, before_write, list);
> + g_slice_free(BDRVBeforeWrite, before_write);
> +}
> diff --git a/include/block/block_int.h b/include/block/block_int.h
> index 6078dd3..e2299df 100644
> --- a/include/block/block_int.h
> +++ b/include/block/block_int.h
> @@ -211,6 +211,16 @@ struct BlockDriver {
> QLIST_ENTRY(BlockDriver) list;
> };
>
> +/**
> + * BDRVBeforeWriteFunc:
> + *
> + * See #bdrv_add_before_write_cb().
> + */
> +typedef void coroutine_fn BDRVBeforeWriteFunc(BlockDriverState *bs,
> + int64_t sector_num, int nb_sectors, QEMUIOVector *qiov);
> +
> +typedef struct BDRVBeforeWrite BDRVBeforeWrite;
> +
> /*
> * Note: the function bdrv_append() copies and swaps contents of
> * BlockDriverStates, so if you add new fields to this struct, please
> @@ -289,6 +299,9 @@ struct BlockDriverState {
> /* long-running background operation */
> BlockJob *job;
>
> + /* Callback before write request is processed */
> + QTAILQ_HEAD(, BDRVBeforeWrite) before_write_cbs;
> +
> QDict *options;
> };
>
> @@ -298,6 +311,25 @@ void bdrv_set_io_limits(BlockDriverState *bs,
> BlockIOLimit *io_limits);
>
> /**
> + * bdrv_add_before_write_cb:
> + *
> + * Register a callback that is invoked before write requests are processed
> but
> + * after any throttling or waiting for overlapping requests.
> + *
> + * Returns: a #BDRVBeforeWrite to use with bdrv_remove_before_write_cb()
> + */
> +BDRVBeforeWrite *bdrv_add_before_write_cb(BlockDriverState *bs,
> + BDRVBeforeWriteFunc *cb);
> +
> +/**
> + * bdrv_remove_before_write_cb:
> + *
> + * Unregister a before write callback.
> + */
> +void bdrv_remove_before_write_cb(BlockDriverState *bs,
> + BDRVBeforeWrite *before_write);
> +
> +/**
> * bdrv_get_aio_context:
> *
> * Returns: the currently bound #AioContext
>
