Re: [Qemu-devel] [PATCH] dump: Show custom message for ENOSPC

[Eric Blake <eblake@redhat.com>]

On 02/09/2018 01:31 PM, Yasmin Beatriz wrote:
> This patch intends to make a more specific message for when
> the system has not enough space to save guest memory.
> 
> Reported-by: yilzhang@redhat.com
> Cc: Jose Ricardo Ziviani <joserz@linux.vnet.ibm.com>
> Signed-off-by: Yasmin Beatriz <yasmins@linux.vnet.ibm.com>
> ---
>   dump.c | 9 ++++++++-
>   1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/dump.c b/dump.c
> index e9dfed060a..eb56ff53f6 100644
> --- a/dump.c
> +++ b/dump.c
> @@ -106,6 +106,9 @@ static int fd_write_vmcore(const void *buf, size_t size, void *opaque)
>   
>       written_size = qemu_write_full(s->fd, buf, size);
>       if (written_size != size) {
> +        if (errno == ENOSPC) {
> +            return -ENOSPC;
> +        }
>           return -1;

Mixing a return of -1 and negative errno is ugly (as -1 is 
indistinguishable from -EPERM on many, but not all, operating systems). 
If you need to distinguish between different error types, then return 
negative errno in all places.

>       }
>   
> @@ -364,7 +367,11 @@ static void write_data(DumpState *s, void *buf, int length, Error **errp)
>   
>       ret = fd_write_vmcore(buf, length, s);
>       if (ret < 0) {
> -        error_setg(errp, "dump: failed to save memory");

Or, if you really want better error messages, it might make sense to 
push errp setting down into fd_write_vmcore() (all callers have to be 
updated).

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