[PATCH RFC] nvmet: fix tmpfs-based backstores support

[Chaitanya Kulkarni]

On 11/17/21 07:24, Maurizio Lombardi wrote:
> External email: Use caution opening links or attachments
> 
> 
> commit 50a909db36f2 ("nvmet: use IOCB_NOWAIT for file-ns buffered I/O")
> optimized the read command behaviour  when buffered file-ns

s/behaviour/behavior

> configurations are used.
> It issues the read commands with the IOCB_NOWAIT flag set to try
> to access the data from the cache.
> 
> However, the patch was buggy because both read and write commands are
> issued with IOCB_NOWAIT, this broke tmpfs-based backstores because tmpfs
> doesn't accept write commands with IOCB_NOWAIT.
> 
> Fix this bug by restricting IOCB_NOWAIT to read commands only.
> 
> Fixes: 50a909db36f2 ("nvmet: use IOCB_NOWAIT for file-ns buffered I/O")
> 
> Signed-off-by: Maurizio Lombardi <mlombard at redhat.com>

We will need blktests for this.

Also, can you share performance numbers with this patch and
the errors that you are getting without this patch ?

> ---
>   drivers/nvme/target/io-cmd-file.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/nvme/target/io-cmd-file.c b/drivers/nvme/target/io-cmd-file.c
> index 6aa30f30b572..1d9b41190583 100644
> --- a/drivers/nvme/target/io-cmd-file.c
> +++ b/drivers/nvme/target/io-cmd-file.c
> @@ -266,6 +266,7 @@ static void nvmet_file_execute_rw(struct nvmet_req *req)
> 
>          if (req->ns->buffered_io) {
>                  if (likely(!req->f.mpool_alloc) &&
> +                               req->cmd->rw.opcode == nvme_cmd_read &&
>                                  nvmet_file_execute_io(req, IOCB_NOWAIT))
>                          return;
>                  nvmet_file_submit_buffered_io(req);
> --
> 2.27.0
>