Re: [Qemu-devel] [PATCH 1/1] Support abstract socket namespace in AF_UNIX socket family.

[Anthony Liguori <anthony@codemonkey.ws>]

Alexander Barabash <alexander_barabash@mentor.com> writes:

> The abstract socket namespace is a nonportable Linux extension.
> The sockets' names in this namespace have no connection
> with file system pathnames. To specify a named AF_UNIX socket
> in the abstract socket namespace, start the socket's path option
> with a backslash followed by zero: \0.
>
> Signed-off-by: Alexander Barabash <alexander_barabash@mentor.com>

Magic interpretation of path names is a bad thing in general.

I think it would be better to add a flag 'abstract=on' which
indicates to use the abstract namespace.  As an example:

qemu -chardev foo,path=bar,abstract=on

vs:

qemu -chardev foo,path="\\\\0bar"

I think the former is quite a bit more user friendly.

Regards,

Anthony Liguori

> ---
>  qemu-sockets.c |   58 +++++++++++++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 55 insertions(+), 3 deletions(-)
>
> diff --git a/qemu-sockets.c b/qemu-sockets.c
> index 3537bf3..70c8ad5 100644
> --- a/qemu-sockets.c
> +++ b/qemu-sockets.c
> @@ -663,11 +663,50 @@ int inet_nonblocking_connect(const char *str,
>  
>  #ifndef _WIN32
>  
> +/*
> + * The abstract socket namespace is a nonportable Linux extension.
> + * The sockets' names in this namespace have no connection
> + * with file system pathnames. To specify a named AF_UNIX socket
> + * in the abstract socket namespace, start the socket's path option
> + * with a backslash followed by zero: \0.
> + */
> +static
> +char *get_abstract_namespace_path(const char *path, int *abstract_path_length)
> +{
> +    char *abstract_path;
> +    char *inp;
> +    char *outp;
> +    char c;
> +
> +    *abstract_path_length = 0;
> +    if ((path == NULL) || (path[0] != '\\') || (path[1] != '0')) {
> +        return NULL;
> +    }
> +    abstract_path = g_strdup(path + 2);
> +    for (inp = abstract_path, outp = abstract_path; (c = *inp); ++inp, ++outp) {
> +        if (c == '\\') {
> +            c = *++inp;
> +            if (c == '\\') {
> +                *outp = c;
> +            } else if (c == '0') {
> +                *outp = '\0';
> +            }
> +        } else {
> +            *outp = c;
> +        }
> +    }
> +    *abstract_path_length = outp - abstract_path;
> +    return abstract_path;
> +}
> +
>  int unix_listen_opts(QemuOpts *opts, Error **errp)
>  {
>      struct sockaddr_un un;
>      const char *path = qemu_opt_get(opts, "path");
> +    int abstract_path_length;
> +    char *abstract_path;
>      int sock, fd;
> +    socklen_t addrlen = sizeof(un);
>  
>      sock = qemu_socket(PF_UNIX, SOCK_STREAM, 0);
>      if (sock < 0) {
> @@ -675,9 +714,18 @@ int unix_listen_opts(QemuOpts *opts, Error **errp)
>          return -1;
>      }
>  
> +    abstract_path = get_abstract_namespace_path(path, &abstract_path_length);
> +
>      memset(&un, 0, sizeof(un));
>      un.sun_family = AF_UNIX;
> -    if (path && strlen(path)) {
> +    if (abstract_path != NULL) {
> +        if (abstract_path_length > sizeof(un.sun_path) - 1) {
> +            abstract_path_length = sizeof(un.sun_path) - 1;
> +        }
> +        memcpy(un.sun_path + 1, abstract_path, abstract_path_length);
> +        addrlen =
> +            offsetof(struct sockaddr_un, sun_path) + 1 + abstract_path_length;
> +    } else if (path && strlen(path)) {
>          snprintf(un.sun_path, sizeof(un.sun_path), "%s", path);
>      } else {
>          char *tmpdir = getenv("TMPDIR");
> @@ -694,8 +742,10 @@ int unix_listen_opts(QemuOpts *opts, Error **errp)
>          qemu_opt_set(opts, "path", un.sun_path);
>      }
>  
> -    unlink(un.sun_path);
> -    if (bind(sock, (struct sockaddr*) &un, sizeof(un)) < 0) {
> +    if (abstract_path == NULL) {
> +        unlink(un.sun_path);
> +    }
> +    if (bind(sock, (struct sockaddr *) &un, addrlen) < 0) {
>          error_set_errno(errp, errno, QERR_SOCKET_BIND_FAILED);
>          goto err;
>      }
> @@ -704,10 +754,12 @@ int unix_listen_opts(QemuOpts *opts, Error **errp)
>          goto err;
>      }
>  
> +    g_free(abstract_path);
>      return sock;
>  
>  err:
>      closesocket(sock);
> +    g_free(abstract_path);
>      return -1;
>  }
>  
> -- 
> 1.7.9.5