From 1bc5f09f2e1b2be8f6f737b8d5352b438fc41492 Mon Sep 17 00:00:00 2001 From: Kevin Wolf Date: Tue, 26 Jun 2018 14:23:23 +0200 Subject: [PATCH] block: Use tracked request for truncate When growing an image, block drivers (especially protocol drivers) may initialise the newly added area. I/O requests to the same area need to wait for this initialisation to be completed so that data writes don't get overwritten and reads don't read uninitialised data. To avoid overhead in the fast I/O path by adding new locking in the protocol drivers and to restrict the impact to requests that actually touch the new area, reuse the existing tracked request infrastructure in block/io.c and mark all discard requests as serialising. With this change, it is safe for protocol drivers to make .bdrv_co_truncate actually asynchronous. Signed-off-by: Kevin Wolf Reviewed-by: Stefan Hajnoczi --- block/io.c | 25 +++++++++++++++++++++++++ include/block/block_int.h | 1 + 2 files changed, 26 insertions(+) diff --git a/block/io.c b/block/io.c index 7e87a42b8e..01a3c4eac5 100644 --- a/block/io.c +++ b/block/io.c @@ -3039,6 +3039,8 @@ int coroutine_fn bdrv_co_truncate(BdrvChild *child, int64_t offset, { BlockDriverState *bs = child->bs; BlockDriver *drv = bs->drv; + BdrvTrackedRequest req; + int64_t old_size, new_bytes; int ret; assert(child->perm & BLK_PERM_RESIZE); @@ -3053,7 +3055,28 @@ int coroutine_fn bdrv_co_truncate(BdrvChild *child, int64_t offset, return -EINVAL; } + old_size = bdrv_getlength(bs); + if (old_size < 0) { + error_setg_errno(errp, -old_size, "Failed to get old image size"); + return old_size; + } + + if (offset > old_size) { + new_bytes = offset - old_size; + } else { + new_bytes = 0; + } + bdrv_inc_in_flight(bs); + tracked_request_begin(&req, bs, offset, new_bytes, BDRV_TRACKED_TRUNCATE); + + /* If we are growing the image and potentially using preallocation for the + * new area, we need to make sure that no write requests are made to it + * concurrently or they might be overwritten by preallocation. */ + if (new_bytes) { + mark_request_serialising(&req, 1); + wait_serialising_requests(&req); + } if (!drv->bdrv_co_truncate) { if (bs->file && drv->is_filter) { @@ -3087,7 +3110,9 @@ int coroutine_fn bdrv_co_truncate(BdrvChild *child, int64_t offset, atomic_inc(&bs->write_gen); out: + tracked_request_end(&req); bdrv_dec_in_flight(bs); + return ret; } diff --git a/include/block/block_int.h b/include/block/block_int.h index 740166a996..af71b414be 100644 --- a/include/block/block_int.h +++ b/include/block/block_int.h @@ -63,6 +63,7 @@ enum BdrvTrackedRequestType { BDRV_TRACKED_READ, BDRV_TRACKED_WRITE, BDRV_TRACKED_DISCARD, + BDRV_TRACKED_TRUNCATE, }; typedef struct BdrvTrackedRequest { -- 2.11.0