Re: [Qemu-devel] [PATCH v3] Add support for fd: protocol

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

On 07/26/2011 08:51 AM, Corey Bryant wrote:

 > +static int raw_open_fd(BlockDriverState *bs, const char *filename, 
int flags)
 > +{
 > +    BDRVRawState *s = bs->opaque;
 > +    const char *fd_str;
 > +    int fd;
 > +
 > +    /* extract the file descriptor - fail if it's not fd: */
 > +    if (!strstart(filename, "fd:",&fd_str)) {
 > +        return -EINVAL;
 > +    }
 > +
 > +    if (!qemu_isdigit(fd_str[0])) {
 > +        /* get fd from monitor */
 > +        fd = qemu_get_fd(fd_str);
 > +        if (fd == -1) {
 > +            return -EBADF;
 > +        }
 > +    } else {
 > +        char *endptr = NULL;
 > +
 > +        fd = strtol(fd_str,&endptr, 10);
 > +        if (*endptr || (fd == 0&&  fd_str == endptr)) {
 > +            return -EBADF;
 > +        }
 > +    }
 > +
 > +    s->fd = fd;
 > +    s->type = FTYPE_FILE;
 > +
 > +    return raw_open_common(bs, filename, flags, 0);
 > +}
 > +
 > +static BlockDriver bdrv_file_fd = {
 > +    .format_name = "file",
 > +    .protocol_name = "fd",
 > +    .instance_size = sizeof(BDRVRawState),
 > +    .bdrv_probe = NULL, /* no probe for protocols */
 > +    .bdrv_file_open = raw_open_fd,
 > +    .bdrv_read = raw_read,
 > +    .bdrv_write = raw_write,
 > +    .bdrv_close = raw_close,
 > +    .bdrv_flush = raw_flush,
 > +    .bdrv_discard = raw_discard,
 > +
 > +    .bdrv_aio_readv = raw_aio_readv,
 > +    .bdrv_aio_writev = raw_aio_writev,
 > +    .bdrv_aio_flush = raw_aio_flush,
 > +
 > +    .bdrv_truncate = raw_truncate,
 > +    .bdrv_getlength = raw_getlength,
 > +
 > +    .create_options = raw_create_options,
 > +};
 > +

I'm a bit unsure of how to support CD-ROM with the fd: protocol.

I don't think use of bdrv_file_fd is an option.  For example, while 
raw_open_fd may work, there is no eject support.

Another approach is to have 2 BlockDriver structs that support the fd 
protocol.  For example, creating a new BlockDriver struct that mirrors 
bdrv_host_cdrom.  So you would have bdrv_host_cdrom_fd with a 
corresponding cdrom_open_fd function.  But that doesn't appear possible 
as it appears that the protocol must be unique among all BlockDriver 
structs.

Do we need to introduce a similar protocol (maybe "cdfd") to support 
passing of CD-ROM file descriptors?