[Nbd] [PATCH 1/3] nbd: support FLUSH requests
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[Nbd] [PATCH 1/3] nbd: support FLUSH requests
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From: Paolo B. <pbo...@re...> - 2013-02-12 16:06:33
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From: Alex Bligh <al...@al...> The NBD device does not support writeback caching, thus it is not safe against power losses unless the client opens the target with O_DSYNC or O_SYNC. Add support for a new flag that the server can pass. If the flag is enabled, we translate REQ_FLUSH requests into the NBD_CMD_FLUSH command. Cc: <nbd...@li...> Cc: Paul Clements <Pau...@st...> Cc: Andrew Morton <ak...@li...> Signed-off-by: Alex Bligh <al...@al...> [ Removed FUA support for reasons similar to those outlined in https://lkml.org/lkml/2010/8/17/234 for virtio - Paolo ] Signed-off-by: Paolo Bonzini <pbo...@re...> --- drivers/block/nbd.c | 22 ++++++++++++++++++++-- include/uapi/linux/nbd.h | 3 ++- 2 files changed, 22 insertions(+), 3 deletions(-) diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c index 043ddcc..5603765 100644 --- a/drivers/block/nbd.c +++ b/drivers/block/nbd.c @@ -98,6 +98,7 @@ static const char *nbdcmd_to_ascii(int cmd) case NBD_CMD_READ: return "read"; case NBD_CMD_WRITE: return "write"; case NBD_CMD_DISC: return "disconnect"; + case NBD_CMD_FLUSH: return "flush"; case NBD_CMD_TRIM: return "trim/discard"; } return "invalid"; @@ -244,8 +245,15 @@ static int nbd_send_req(struct nbd_device *nbd, struct request *req) request.magic = htonl(NBD_REQUEST_MAGIC); request.type = htonl(nbd_cmd(req)); - request.from = cpu_to_be64((u64)blk_rq_pos(req) << 9); - request.len = htonl(size); + + if (nbd_cmd(req) == NBD_CMD_FLUSH) { + /* Other values are reserved for FLUSH requests. */ + request.from = 0; + request.len = 0; + } else { + request.from = cpu_to_be64((u64)blk_rq_pos(req) << 9); + request.len = htonl(size); + } memcpy(request.handle, &req, sizeof(req)); dprintk(DBG_TX, "%s: request %p: sending control (%s@%llu,%uB)\n", @@ -482,6 +490,11 @@ static void nbd_handle_req(struct nbd_device *nbd, struct request *req) } } + if (req->cmd_flags & REQ_FLUSH) { + BUG_ON(unlikely(blk_rq_sectors(req))); + nbd_cmd(req) = NBD_CMD_FLUSH; + } + req->errors = 0; mutex_lock(&nbd->tx_lock); @@ -684,6 +697,10 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd, if (nbd->flags & NBD_FLAG_SEND_TRIM) queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, nbd->disk->queue); + if (nbd->flags & NBD_FLAG_SEND_FLUSH) + blk_queue_flush(nbd->disk->queue, REQ_FLUSH); + else + blk_queue_flush(nbd->disk->queue, 0); thread = kthread_create(nbd_thread, nbd, nbd->disk->disk_name); if (IS_ERR(thread)) { @@ -705,6 +722,7 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd, queue_flag_clear_unlocked(QUEUE_FLAG_DISCARD, nbd->disk->queue); if (file) fput(file); + nbd->flags = 0; nbd->bytesize = 0; bdev->bd_inode->i_size = 0; set_capacity(nbd->disk, 0); diff --git a/include/uapi/linux/nbd.h b/include/uapi/linux/nbd.h index dfb5144..4f52549 100644 --- a/include/uapi/linux/nbd.h +++ b/include/uapi/linux/nbd.h @@ -33,13 +33,14 @@ enum { NBD_CMD_READ = 0, NBD_CMD_WRITE = 1, NBD_CMD_DISC = 2, - /* there is a gap here to match userspace */ + NBD_CMD_FLUSH = 3, NBD_CMD_TRIM = 4 }; /* values for flags field */ #define NBD_FLAG_HAS_FLAGS (1 << 0) /* nbd-server supports flags */ #define NBD_FLAG_READ_ONLY (1 << 1) /* device is read-only */ +#define NBD_FLAG_SEND_FLUSH (1 << 2) /* can flush writeback cache */ /* there is a gap here to match userspace */ #define NBD_FLAG_SEND_TRIM (1 << 5) /* send trim/discard */ -- 1.7.1 |
