Re: [PATCH ssh v2] ssh: Do not switch session to non-blocking mode

[Michael Tokarev]

13.11.2024 15:55, Richard W.M. Jones wrote:
> From: Jakub Jelen <jjelen@redhat.com>
>
> The libssh does not handle non-blocking mode in SFTP correctly. The
> driver code already changes the mode to blocking for the SFTP
> initialization, but for some reason changes to non-blocking mode.
> This used to work accidentally until libssh in 0.11 branch merged
> the patch to avoid infinite looping in case of network errors:
>
> https://gitlab.com/libssh/libssh-mirror/-/merge_requests/498
>
> Since then, the ssh driver in qemu fails to read files over SFTP
> as the first SFTP messages exchanged after switching the session
> to non-blocking mode return SSH_AGAIN, but that message is lost
> int the SFTP internals and interpretted as SSH_ERROR, which is
> returned to the caller:
>
> https://gitlab.com/libssh/libssh-mirror/-/issues/280
>
> This is indeed an issue in libssh that we should address in the
> long term, but it will require more work on the internals. For
> now, the SFTP is not supported in non-blocking mode.
>
> Fixes: https://gitlab.com/libssh/libssh-mirror/-/issues/280
> Signed-off-by: Jakub Jelen <jjelen@redhat.com>
> Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
> ---
>   block/ssh.c | 3 ---
>   1 file changed, 3 deletions(-)
>
> diff --git a/block/ssh.c b/block/ssh.c
> index 9f8140bcb6..b9f33ec739 100644
> --- a/block/ssh.c
> +++ b/block/ssh.c
> @@ -866,9 +866,6 @@ static int ssh_open(BlockDriverState *bs, QDict *options, 
> int bdrv_flags,
>           goto err;
>       }
>   
> -    /* Go non-blocking. */
> -    ssh_set_blocking(s->session, 0);
> -
>       if (s->attrs->type == SSH_FILEXFER_TYPE_REGULAR) {
>           bs->supported_truncate_flags = BDRV_REQ_ZERO_WRITE;
>       }

I'm picking this up for the next stable series, since new libssh
is being released and used.  Hopefully the resulting code wont
break with old libssh.

Thanks,

/mjt