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



Am 11.08.2011 18:28, schrieb Corey Bryant:
> 
> 
> 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?

I would try to avoid that. I think you can determine the kind of device
during fd_open and then implement an fd_eject etc. that checks this type
and calls the appropriate ioctl. Maybe the same should be done for
file/host_device/host_cdrom instead of having separate protocols.

Anyway, I don't think this is important to get a first version merged.
It will still take a while anyway until we have full support that
libvirt would want to use.

Kevin


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