john cooper wrote:
> I'm all for putting this issue to rest, but if we're
> going to live with an ioctl interface retrieving the
> id string, let's make it a little more friendly from
> the user's perspective.
The qemu side of the patch is ok as-is. The guest-user
interface issue is contained in the driver. While I
see the example ioctl patch has been incorporated into
the virtio_blk driver, there can be no data retrieved
through this interface as virtblk_get_id() will fail
without the qemu counterpart. So we can clean up the
details without concern of existing usage.
The only difference (as above) is allowing the caller
to pass a buffer size to the driver and the driver
informing the caller of the total number of bytes
available:
#include <stdio.h>
#include <strings.h>
#include <fcntl.h>
#define IOCTL_CMD 'VBID'
#define BUFSZ 10
main()
{
int fd, rv;
char buf[255];
bzero(buf, sizeof (buf));
buf[0] = BUFSZ;
if ((fd = open("/dev/vda", O_RDONLY)) < 0)
perror("open");
else if ((rv = ioctl(fd, IOCTL_CMD, buf)) < 0)
perror("ioctl");
else
printf("[%s] %d of %d bytes\n", buf,
BUFSZ < rv ? BUFSZ : rv, rv);
}
Signed-off-by: john cooper <john.coo...@redhat.com>
---
diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 83fa09a..6237732 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -225,15 +225,29 @@ static int virtblk_ioctl(struct block_device *bdev,
fmode_t mode,
struct gendisk *disk = bdev->bd_disk;
struct virtio_blk *vblk = disk->private_data;
+ /* user passes the address of a char[] for return of the id string
+ * and has set char[0] to the array size. copy id string to this
+ * char[] and return the number of non-nul characters in the internal
+ * id string. The caller can then determine if all were received.
+ */
if (cmd == 0x56424944) { /* 'VBID' */
void __user *usr_data = (void __user *)data;
char id_str[VIRTIO_BLK_ID_BYTES];
- int err;
-
- err = virtblk_get_id(disk, id_str);
- if (!err && copy_to_user(usr_data, id_str, VIRTIO_BLK_ID_BYTES))
- err = -EFAULT;
- return err;
+ unsigned char idlen;
+ int rv;
+
+ if (copy_from_user(&idlen, usr_data, sizeof (idlen)))
+ return -EFAULT;
+ if (VIRTIO_BLK_ID_BYTES < idlen)
+ idlen = VIRTIO_BLK_ID_BYTES;
+ if ((rv = virtblk_get_id(disk, id_str)))
+ return rv;
+ if (copy_to_user(usr_data, id_str, idlen))
+ return -EFAULT;
+ for (rv = 0; rv < VIRTIO_BLK_ID_BYTES; ++rv)
+ if (!id_str[rv])
+ break;
+ return rv;
}
/*
* Only allow the generic SCSI ioctls if the host can support it.
--
john.coo...@redhat.com
