Re: [Qemu-devel] [PATCH v5] qemu-config: Add new -add-fd command line option

[Corey Bryant <coreyb@linux.vnet.ibm.com>]

On 10/22/2012 10:36 AM, Kevin Wolf wrote:
> From: Corey Bryant <coreyb@linux.vnet.ibm.com>
>
> This option can be used for passing file descriptors on the
> command line.  It mirrors the existing add-fd QMP command which
> allows an fd to be passed to QEMU via SCM_RIGHTS and added to an
> fd set.
>
> This can be combined with commands such as -drive to link file
> descriptors in an fd set to a drive:
>
>      qemu-kvm -add-fd fd=3,set=2,opaque="rdwr:/path/to/file"
>               -add-fd fd=4,set=2,opaque="rdonly:/path/to/file"
>               -drive file=/dev/fdset/2,index=0,media=disk
>
> This example adds dups of fds 3 and 4, and the accompanying opaque
> strings to the fd set with ID=2.  qemu_open() already knows how
> to handle a filename of this format.  qemu_open() searches the
> corresponding fd set for an fd and when it finds a match, QEMU
> goes on to use a dup of that fd just like it would have used an
> fd that it opened itself.
>
> Signed-off-by: Corey Bryant <coreyb@linux.vnet.ibm.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>
> Sorry, Corey, hope you're okay with me taking over your patch... Your patch was
> against the unmodified version while I already did some changes after the v4
> review, so it didn't apply.
>

That's fine.  Thanks for the hand.

> This version just completely disables fd passing on Windows as I don't think
> it works there anyway. Gives you a nice error message instead of a silently
> ignored -add-fd option.
>
> Also added the missing break for case QEMU_OPTION_add_fd.
>
>   qemu-config.c   |   22 +++++++++++++
>   qemu-options.hx |   36 +++++++++++++++++++++
>   vl.c            |   94 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>   3 files changed, 152 insertions(+), 0 deletions(-)
>
> diff --git a/qemu-config.c b/qemu-config.c
> index cd1ec21..601237d 100644
> --- a/qemu-config.c
> +++ b/qemu-config.c
> @@ -653,6 +653,27 @@ QemuOptsList qemu_boot_opts = {
>       },
>   };
>
> +static QemuOptsList qemu_add_fd_opts = {
> +    .name = "add-fd",
> +    .head = QTAILQ_HEAD_INITIALIZER(qemu_add_fd_opts.head),
> +    .desc = {
> +        {
> +            .name = "fd",
> +            .type = QEMU_OPT_NUMBER,
> +            .help = "file descriptor of which a duplicate is added to fd set",
> +        },{
> +            .name = "set",
> +            .type = QEMU_OPT_NUMBER,
> +            .help = "ID of the fd set to add fd to",
> +        },{
> +            .name = "opaque",
> +            .type = QEMU_OPT_STRING,
> +            .help = "free-form string used to describe fd",
> +        },
> +        { /* end of list */ }
> +    },
> +};
> +
>   static QemuOptsList *vm_config_groups[32] = {
>       &qemu_drive_opts,
>       &qemu_chardev_opts,
> @@ -669,6 +690,7 @@ static QemuOptsList *vm_config_groups[32] = {
>       &qemu_boot_opts,
>       &qemu_iscsi_opts,
>       &qemu_sandbox_opts,
> +    &qemu_add_fd_opts,
>       NULL,
>   };
>
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 46f0539..a67a255 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -253,6 +253,14 @@ qemu-system-i386 -drive file=file,index=2,media=disk
>   qemu-system-i386 -drive file=file,index=3,media=disk
>   @end example
>
> +You can open an image using pre-opened file descriptors from an fd set:
> +@example
> +qemu-system-i386
> +-add-fd fd=3,set=2,opaque="rdwr:/path/to/file"
> +-add-fd fd=4,set=2,opaque="rdonly:/path/to/file"
> +-drive file=/dev/fdset/2,index=0,media=disk
> +@end example
> +
>   You can connect a CDROM to the slave of ide0:
>   @example
>   qemu-system-i386 -drive file=file,if=ide,index=1,media=cdrom
> @@ -285,6 +293,34 @@ qemu-system-i386 -hda a -hdb b
>   @end example
>   ETEXI
>
> +DEF("add-fd", HAS_ARG, QEMU_OPTION_add_fd,
> +    "-add-fd fd=fd,set=set[,opaque=opaque]\n"
> +    "                Add 'fd' to fd 'set'\n", QEMU_ARCH_ALL)
> +STEXI
> +@item -add-fd fd=@var{fd},set=@var{set}[,opaque=@var{opaque}]
> +@findex -add-fd
> +
> +Add a file descriptor to an fd set.  Valid options are:
> +
> +@table @option
> +@item fd=@var{fd}
> +This option defines the file descriptor of which a duplicate is added to fd set.
> +The file descriptor cannot be stdin, stdout, or stderr.
> +@item set=@var{set}
> +This option defines the ID of the fd set to add the file descriptor to.
> +@item opaque=@var{opaque}
> +This option defines a free-form string that can be used to describe @var{fd}.
> +@end table
> +
> +You can open an image using pre-opened file descriptors from an fd set:
> +@example
> +qemu-system-i386
> +-add-fd fd=3,set=2,opaque="rdwr:/path/to/file"
> +-add-fd fd=4,set=2,opaque="rdonly:/path/to/file"
> +-drive file=/dev/fdset/2,index=0,media=disk
> +@end example
> +ETEXI
> +
>   DEF("set", HAS_ARG, QEMU_OPTION_set,
>       "-set group.id.arg=value\n"
>       "                set <arg> parameter for item <id> of type <group>\n"
> diff --git a/vl.c b/vl.c
> index ee3c43a..b870caf 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -790,6 +790,78 @@ static int parse_sandbox(QemuOpts *opts, void *opaque)
>       return 0;
>   }
>
> +#ifndef _WIN32
> +static int parse_add_fd(QemuOpts *opts, void *opaque)
> +{
> +    int fd, dupfd, flags;
> +    int64_t fdset_id;
> +    const char *fd_opaque = NULL;
> +
> +    fd = qemu_opt_get_number(opts, "fd", -1);
> +    fdset_id = qemu_opt_get_number(opts, "set", -1);
> +    fd_opaque = qemu_opt_get(opts, "opaque");
> +
> +    if (fd < 0) {
> +        qerror_report(ERROR_CLASS_GENERIC_ERROR,
> +                      "fd option is required and must be non-negative");
> +        return -1;
> +    }
> +
> +    if (fd <= STDERR_FILENO) {
> +        qerror_report(ERROR_CLASS_GENERIC_ERROR,
> +                      "fd cannot be a standard I/O stream");
> +        return -1;
> +    }
> +
> +    /*
> +     * All fds inherited across exec() necessarily have FD_CLOEXEC
> +     * clear, while qemu sets FD_CLOEXEC on all other fds used internally.
> +     */
> +    flags = fcntl(fd, F_GETFD);
> +    if (flags == -1 || (flags & FD_CLOEXEC)) {
> +        qerror_report(ERROR_CLASS_GENERIC_ERROR,
> +                      "fd is not valid or already in use");
> +        return -1;
> +    }
> +
> +    if (fdset_id < 0) {
> +        qerror_report(ERROR_CLASS_GENERIC_ERROR,
> +                      "set option is required and must be non-negative");
> +        return -1;
> +    }
> +
> +#ifdef F_DUPFD_CLOEXEC
> +    dupfd = fcntl(fd, F_DUPFD_CLOEXEC, 0);
> +#else
> +    dupfd = dup(fd);
> +    if (dupfd != -1) {
> +        qemu_set_cloexec(dupfd);
> +    }
> +#endif
> +    if (dupfd == -1) {
> +        qerror_report(ERROR_CLASS_GENERIC_ERROR,
> +                      "Error duplicating fd: %s", strerror(errno));
> +        return -1;
> +    }
> +
> +    /* add the duplicate fd, and optionally the opaque string, to the fd set */
> +    monitor_fdset_add_fd(dupfd, true, fdset_id, fd_opaque ? true : false,
> +                         fd_opaque, NULL);
> +
> +    return 0;
> +}
> +
> +static int cleanup_add_fd(QemuOpts *opts, void *opaque)
> +{
> +    int fd;
> +
> +    fd = qemu_opt_get_number(opts, "fd", -1);
> +    close(fd);
> +
> +    return 0;
> +}
> +#endif
> +
>   /***********************************************************/
>   /* QEMU Block devices */
>
> @@ -3309,6 +3381,18 @@ int main(int argc, char **argv, char **envp)
>                       exit(0);
>                   }
>                   break;
> +            case QEMU_OPTION_add_fd:
> +#ifndef _WIN32
> +                opts = qemu_opts_parse(qemu_find_opts("add-fd"), optarg, 0);
> +                if (!opts) {
> +                    exit(0);
> +                }
> +#else
> +                error_report("File descriptor passing is disabled on this "
> +                             "platform");
> +                exit(1);
> +#endif
> +                break;
>               default:
>                   os_parse_cmd_args(popt->index, optarg);
>               }
> @@ -3320,6 +3404,16 @@ int main(int argc, char **argv, char **envp)
>           exit(1);
>       }
>
> +#ifndef _WIN32
> +    if (qemu_opts_foreach(qemu_find_opts("add-fd"), parse_add_fd, NULL, 1)) {
> +        exit(1);
> +    }
> +
> +    if (qemu_opts_foreach(qemu_find_opts("add-fd"), cleanup_add_fd, NULL, 1)) {
> +        exit(1);
> +    }
> +#endif
> +
>       if (machine == NULL) {
>           fprintf(stderr, "No machine found.\n");
>           exit(1);
>

This looks good to me.

-- 
Regards,
Corey Bryant