Re: [Qemu-devel] [PATCH] scsi: turn "is this a SCSI device?" into a conditional hint

[Eric Blake <eblake@redhat.com>]

On 03/21/2018 05:58 AM, Paolo Bonzini wrote:
> If the user does not have permissions to send ioctls to the device (due to
> SELinux or cgroups, for example), the output can look like
> 
> qemu-kvm: -device scsi-block,drive=disk: cannot get SG_IO version number:
>    Operation not permitted.  Is this a SCSI device?
> 
> but this is confusing because the ioctl was blocked _before_ the device
> even received the SG_GET_VERSION_NUM ioctl.  Therefore, for EPERM errors
> the suggestion should be eliminated.  To make that simpler, change the
> code to use error_append_hint.
> 
> Reported-by: Ala Hino <ahino@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>   hw/scsi/scsi-disk.c    | 7 ++++---
>   hw/scsi/scsi-generic.c | 7 ++++---
>   2 files changed, 8 insertions(+), 6 deletions(-)
> 

> +++ b/hw/scsi/scsi-disk.c
> @@ -2637,9 +2637,10 @@ static void scsi_block_realize(SCSIDevice *dev, Error **errp)
>       /* check we are using a driver managing SG_IO (version 3 and after) */
>       rc = blk_ioctl(s->qdev.conf.blk, SG_GET_VERSION_NUM, &sg_version);
>       if (rc < 0) {
> -        error_setg(errp, "cannot get SG_IO version number: %s.  "
> -                     "Is this a SCSI device?",
> -                     strerror(-rc));
> +        error_setg(errp, "cannot get SG_IO version number: %s", strerror(-rc));
> +        if (rc != -EPERM) {
> +            error_append_hint(errp, "Is this a SCSI device?");

Missing the \n (error_append_hint does NOT automatically add one, 
because sometimes hints are pieced together but should still display in 
one line).

> +++ b/hw/scsi/scsi-generic.c
> @@ -500,9 +500,10 @@ static void scsi_generic_realize(SCSIDevice *s, Error **errp)
>       /* check we are using a driver managing SG_IO (version 3 and after */
>       rc = blk_ioctl(s->conf.blk, SG_GET_VERSION_NUM, &sg_version);
>       if (rc < 0) {
> -        error_setg(errp, "cannot get SG_IO version number: %s.  "
> -                         "Is this a SCSI device?",
> -                         strerror(-rc));
> +        error_setg(errp, "cannot get SG_IO version number: %s", strerror(-rc));
> +        if (rc != -EPERM) {
> +            error_append_hint(errp, "Is this a SCSI device?");

And again.  With that fixed,
Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org