Re: [PATCH v3 4/4] block: switch to use qemu_open/qemu_create for improved errors

[Eric Blake]

On 7/24/20 8:25 AM, Daniel P. Berrangé wrote:
> Currently at startup if using cache=none on a filesystem lacking
> O_DIRECT such as tmpfs, at startup QEMU prints
>
> qemu-system-x86_64: -drive file=/tmp/foo.img,cache=none: file system may not 
> support O_DIRECT
> qemu-system-x86_64: -drive file=/tmp/foo.img,cache=none: Could not open 
> '/tmp/foo.img': Invalid argument

Are we trying to get this in 5.1?

> while at QMP level the hint is missing, so QEMU reports just
>
>    "error": {
>        "class": "GenericError",
>        "desc": "Could not open '/tmp/foo.img': Invalid argument"
>    }
>
> which is close to useless for the end user trying to figure out what
> they did wrong.
>
> With this change at startup QEMU prints
>
> qemu-system-x86_64: -drive file=/tmp/foo.img,cache=none: Unable to open 
> '/tmp/foo.img' flags 0x4000: filesystem does not support O_DIRECT
>
> while at the QMP level QEMU reports a massively more informative
>
>    "error": {
>       "class": "GenericError",
>       "desc": "Unable to open '/tmp/foo.img' flags 0x4002: filesystem does not 
> support O_DIRECT"
>    }
>
> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> ---

> @@ -3335,7 +3331,7 @@ static bool setup_cdrom(char *bsd_path, Error **errp)
>       for (index = 0; index < num_of_test_partitions; index++) {
>           snprintf(test_partition, sizeof(test_partition), "%ss%d", bsd_path,
>                    index);
> -        fd = qemu_open_old(test_partition, O_RDONLY | O_BINARY | O_LARGEFILE);
> +        fd = qemu_open(test_partition, O_RDONLY | O_BINARY | O_LARGEFILE, 
> NULL);

Should qemu_open() always be setting O_BINARY|O_LARGEFILE, without us 
having to worry about them at each caller?  But that's a separate cleanup.

Reviewed-by: Eric Blake <eblake@redhat.com>

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org