Re: [PATCH v2 11/11] tools/libvchan: libxenvchan_client_init: use ENOENT for no server - Marek Marczykowski-Górecki

From: "Marek Marczykowski-Górecki" <marmarek@invisiblethingslab.com>
To: Ian Jackson <ian.jackson@eu.citrix.com>
Cc: xen-devel@lists.xenproject.org, Wei Liu <wei.liu2@citrix.com>
Subject: Re: [PATCH v2 11/11] tools/libvchan: libxenvchan_client_init: use ENOENT for no server
Date: Sat, 10 Nov 2018 10:06:47 +0100	[thread overview]
Message-ID: <20181110090647.GC4051@mail-itl> (raw)
In-Reply-To: <20181108170805.12774-12-ian.jackson@eu.citrix.com>

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On Thu, Nov 08, 2018 at 05:08:05PM +0000, Ian Jackson wrote:
> * Promise that we will set errno to ENOENT if the server is not
>   yet set up.
> * Arrange that all ENOENT returns other than from the read of ring-ref
>   are turned into EIO, logging when we do so.
> 
> Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
> CC: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>

Since xtl_log now accepts NULL, it should be fine. Thanks!
Reviewed-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>

> ---
>  tools/libvchan/init.c        | 11 ++++++++++-
>  tools/libvchan/libxenvchan.h |  4 ++++
>  2 files changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/libvchan/init.c b/tools/libvchan/init.c
> index d987acd338..e58f6bf9ac 100644
> --- a/tools/libvchan/init.c
> +++ b/tools/libvchan/init.c
> @@ -45,6 +45,7 @@
>  #include <xen/sys/gntalloc.h>
>  #include <xen/sys/gntdev.h>
>  #include <libxenvchan.h>
> +#include <xentoollog.h>
>  
>  #ifndef PAGE_SHIFT
>  #define PAGE_SHIFT 12
> @@ -419,7 +420,7 @@ struct libxenvchan *libxenvchan_client_init(struct xentoollog_logger *logger,
>  	snprintf(buf, sizeof buf, "%s/ring-ref", xs_path);
>  	ref = xs_read(xs, 0, buf, &len);
>  	if (!ref)
> -		goto fail;
> +		goto fail_allow_enoent;
>  	ring_ref = atoi(ref);
>  	free(ref);
>  	if (!ring_ref)
> @@ -452,7 +453,15 @@ struct libxenvchan *libxenvchan_client_init(struct xentoollog_logger *logger,
>  	if (xs)
>  		xs_daemon_close(xs);
>  	return ctrl;
> +
>   fail:
> +	if (errno == ENOENT) {
> +		xtl_log(logger, XTL_ERROR, errno, "vchan",
> +			"error talking to server `%s', returning EIO",
> +			xs_path);
> +		errno = EIO;
> +	}
> + fail_allow_enoent:
>  	libxenvchan_close(ctrl);
>  	ctrl = NULL;
>  	goto out;
> diff --git a/tools/libvchan/libxenvchan.h b/tools/libvchan/libxenvchan.h
> index e4ccca1ff0..8a4ec2ce4c 100644
> --- a/tools/libvchan/libxenvchan.h
> +++ b/tools/libvchan/libxenvchan.h
> @@ -105,6 +105,10 @@ struct libxenvchan *libxenvchan_server_init(struct xentoollog_logger *logger,
>   * safely, however no locking is performed, so you must prevent multiple clients
>   * from connecting to a single server.
>   *
> + * Failing with ENOENT means the server has not yet called
> + * libxenvchan_server_init, You may wait for a server to appear by
> + * setting a xenstore watch on xs_path.
> + *
>   * @param logger Logger for libxc errors
>   * @param domain The peer domain to connect to
>   * @param xs_path Base xenstore path for storing ring/event data

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?

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