[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [PATCH v2 1/4] block: nbd: Fix convert qcow2 compressed to nbd

From: Eric Blake
Subject: Re: [PATCH v2 1/4] block: nbd: Fix convert qcow2 compressed to nbd
Date: Tue, 28 Jul 2020 09:30:57 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0

On 7/28/20 8:15 AM, Vladimir Sementsov-Ogievskiy wrote:
28.07.2020 00:58, Nir Soffer wrote:
When converting to qcow2 compressed format, the last step is a special
zero length compressed write, ending in call to bdrv_co_truncate(). This
call always fails for the nbd driver since it does not implement

+static int coroutine_fn nbd_co_truncate(BlockDriverState *bs, int64_t offset, +                                        bool exact, PreallocMode prealloc, +                                        BdrvRequestFlags flags, Error **errp)
+    BDRVNBDState *s = bs->opaque;
+    if (offset != s->info.size && exact) {
+        error_setg(errp, "Cannot resize NBD nodes");
+        return -ENOTSUP;
+    }
+    if (offset > s->info.size) {
+        error_setg(errp, "Cannot grow NBD nodes");
+        return -EINVAL;
+    }

I think that ENOTSUP actually is valid error code for both cases.. NBD protocol has experimental extension NBD_CMD_RESIZE, so one day we'll implement this. So, I think, it's not invalid, but just not supported yet. Still, not a big deal, so with ENOTSUP or EINVAL:
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

Indeed, if we ever get around to fully specifying how NBD_CMD_RESIZE should even work, we'll be revisiting this code to implement that.

Also, may be better to manage it in generic layer:
If driver doesn't implement bdrv_co_truncate handler (or return ENOTSUP), and we are truncating to the same size, or to smaller size with exact=false, we just report success? Then we'll drop same code from file-posix.c

That was also my question on v1; but given the closeness to the release, this is a minimal change appropriate for -rc2, while changing the generic layer may have unintended consequences.

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

reply via email to

[Prev in Thread] Current Thread [Next in Thread]