From 2b556518c3424caa4f40ee4f6199e8877488f5e8 Mon Sep 17 00:00:00 2001 From: Kevin Wolf Date: Thu, 10 Mar 2016 14:01:31 +0100 Subject: nbd: Support BDRV_REQ_FUA The NBD server already used to send a FUA flag when the writethrough mode was set. This code was a remnant from the times where protocol drivers actually had to implement writethrough modes. Since nowadays the block layer sends flushes in writethrough mode and non-root nodes are always writeback, this was mostly dead code - only mostly because if NBD was configured to be used without a format, we sent _both_ FUA and an explicit flush afterwards, which makes the code not technically dead, but useless overhead. This patch changes the code so that the block layer's FUA flag is recognised and translated into a NBD FUA flag. The additional flush is avoided now. Signed-off-by: Kevin Wolf Reviewed-by: Max Reitz --- block/nbd.c | 27 ++++++++++++++++++++++++++- 1 file changed, 26 insertions(+), 1 deletion(-) (limited to 'block/nbd.c') diff --git a/block/nbd.c b/block/nbd.c index 896064a131..f7ea3b3608 100644 --- a/block/nbd.c +++ b/block/nbd.c @@ -355,10 +355,29 @@ static int nbd_co_readv(BlockDriverState *bs, int64_t sector_num, return nbd_client_co_readv(bs, sector_num, nb_sectors, qiov); } +static int nbd_co_writev_flags(BlockDriverState *bs, int64_t sector_num, + int nb_sectors, QEMUIOVector *qiov, int flags) +{ + int ret; + + ret = nbd_client_co_writev(bs, sector_num, nb_sectors, qiov, &flags); + if (ret < 0) { + return ret; + } + + /* The flag wasn't sent to the server, so we need to emulate it with an + * explicit flush */ + if (flags & BDRV_REQ_FUA) { + ret = nbd_client_co_flush(bs); + } + + return ret; +} + static int nbd_co_writev(BlockDriverState *bs, int64_t sector_num, int nb_sectors, QEMUIOVector *qiov) { - return nbd_client_co_writev(bs, sector_num, nb_sectors, qiov); + return nbd_co_writev_flags(bs, sector_num, nb_sectors, qiov, 0); } static int nbd_co_flush(BlockDriverState *bs) @@ -458,6 +477,8 @@ static BlockDriver bdrv_nbd = { .bdrv_file_open = nbd_open, .bdrv_co_readv = nbd_co_readv, .bdrv_co_writev = nbd_co_writev, + .bdrv_co_writev_flags = nbd_co_writev_flags, + .supported_write_flags = BDRV_REQ_FUA, .bdrv_close = nbd_close, .bdrv_co_flush_to_os = nbd_co_flush, .bdrv_co_discard = nbd_co_discard, @@ -476,6 +497,8 @@ static BlockDriver bdrv_nbd_tcp = { .bdrv_file_open = nbd_open, .bdrv_co_readv = nbd_co_readv, .bdrv_co_writev = nbd_co_writev, + .bdrv_co_writev_flags = nbd_co_writev_flags, + .supported_write_flags = BDRV_REQ_FUA, .bdrv_close = nbd_close, .bdrv_co_flush_to_os = nbd_co_flush, .bdrv_co_discard = nbd_co_discard, @@ -494,6 +517,8 @@ static BlockDriver bdrv_nbd_unix = { .bdrv_file_open = nbd_open, .bdrv_co_readv = nbd_co_readv, .bdrv_co_writev = nbd_co_writev, + .bdrv_co_writev_flags = nbd_co_writev_flags, + .supported_write_flags = BDRV_REQ_FUA, .bdrv_close = nbd_close, .bdrv_co_flush_to_os = nbd_co_flush, .bdrv_co_discard = nbd_co_discard, -- cgit v1.2.3