[PATCH 0/1] RFC: implement reopen for nbd driver

[PATCH 0/1] RFC: implement reopen for nbd driver

[Maxim Levitsky]

Hi,
It looks like nbd driver doesn't have support
for reopen, which doesn't allow to commit qcow2 snapshots
which have nbd export as a base file.
This is because the base is opened read-only, and only
when commit job starts it reopens the base read-write.

Now after talking with Eric Blake, I understood that
nbd doesn't have the ability to tell the server to open read/only
and then change this on the fly, thus even when opening
an export as read-only the server will still allow writes.

This means that an empty .bdrv_reopen_prepare
(well except checking that export is not read-only) is supposed
to be enough.

Sending this as RFC, since I am not sure that this is the correct
solution.

Best regards,
	Maxim Levitsky

Maxim Levitsky (1):
  nbd: add empty .bdrv_reopen_prepare

 block/nbd.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

-- 
2.17.2

[PATCH 1/1] nbd: add empty .bdrv_reopen_prepare

[Maxim Levitsky]

Fixes commit job / qemu-img commit, when
commiting qcow2 file which is based on nbd export.


Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1718727

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
---
 block/nbd.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/block/nbd.c b/block/nbd.c
index 813c40d8f0..fd78e5f330 100644
--- a/block/nbd.c
+++ b/block/nbd.c
@@ -1158,6 +1158,18 @@ static int coroutine_fn nbd_client_co_block_status(
         BDRV_BLOCK_OFFSET_VALID;
 }
 
+static int nbd_client_reopen_prepare(BDRVReopenState *state,
+                                     BlockReopenQueue *queue, Error **errp)
+{
+    BDRVNBDState *s = (BDRVNBDState *)state->bs->opaque;
+
+    if ((state->flags & BDRV_O_RDWR) && (s->info.flags & NBD_FLAG_READ_ONLY)) {
+        error_setg(errp, "Can't reopen read-only NBD mount as read/write");
+        return -EACCES;
+    }
+    return 0;
+}
+
 static void nbd_client_close(BlockDriverState *bs)
 {
     BDRVNBDState *s = (BDRVNBDState *)bs->opaque;
@@ -1798,6 +1810,7 @@ static BlockDriver bdrv_nbd = {
     .instance_size              = sizeof(BDRVNBDState),
     .bdrv_parse_filename        = nbd_parse_filename,
     .bdrv_file_open             = nbd_open,
+    .bdrv_reopen_prepare        = nbd_client_reopen_prepare,
     .bdrv_co_preadv             = nbd_client_co_preadv,
     .bdrv_co_pwritev            = nbd_client_co_pwritev,
     .bdrv_co_pwrite_zeroes      = nbd_client_co_pwrite_zeroes,
@@ -1820,6 +1833,7 @@ static BlockDriver bdrv_nbd_tcp = {
     .instance_size              = sizeof(BDRVNBDState),
     .bdrv_parse_filename        = nbd_parse_filename,
     .bdrv_file_open             = nbd_open,
+    .bdrv_reopen_prepare        = nbd_client_reopen_prepare,
     .bdrv_co_preadv             = nbd_client_co_preadv,
     .bdrv_co_pwritev            = nbd_client_co_pwritev,
     .bdrv_co_pwrite_zeroes      = nbd_client_co_pwrite_zeroes,
@@ -1842,6 +1856,7 @@ static BlockDriver bdrv_nbd_unix = {
     .instance_size              = sizeof(BDRVNBDState),
     .bdrv_parse_filename        = nbd_parse_filename,
     .bdrv_file_open             = nbd_open,
+    .bdrv_reopen_prepare        = nbd_client_reopen_prepare,
     .bdrv_co_preadv             = nbd_client_co_preadv,
     .bdrv_co_pwritev            = nbd_client_co_pwritev,
     .bdrv_co_pwrite_zeroes      = nbd_client_co_pwrite_zeroes,
-- 
2.17.2

Re: [PATCH 1/1] nbd: add empty .bdrv_reopen_prepare

[Max Reitz]

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On 30.09.19 23:38, Maxim Levitsky wrote:
> Fixes commit job / qemu-img commit, when
> commiting qcow2 file which is based on nbd export.
> 
> 
> Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1718727
> 
> Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> ---
>  block/nbd.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)

Thanks, applied to my block branch:

https://git.xanclic.moe/XanClic/qemu/commits/branch/block

Max


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Re: [PATCH 0/1] RFC: implement reopen for nbd driver

[no-reply]

Patchew URL: https://patchew.org/QEMU/20190930213820.29777-1-mlevitsk@redhat.com/



Hi,

This series failed the asan build test. Please find the testing commands and
their output below. If you have Docker installed, you can probably reproduce it
locally.

=== TEST SCRIPT BEGIN ===
#!/bin/bash
export ARCH=x86_64
make docker-image-fedora V=1 NETWORK=1
time make docker-test-debug@fedora TARGET_LIST=x86_64-softmmu J=14 NETWORK=1
=== TEST SCRIPT END ===




The full log is available at
http://patchew.org/logs/20190930213820.29777-1-mlevitsk@redhat.com/testing.asan/?type=message.
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