On Tue, May 07, 2019 at 08:34:51AM +0200, Markus Armbruster wrote:
> Cc: Peter for a libvirt perspective.
>
> Stefano Garzarella <sgarz...@redhat.com> writes:
>
> > This patch adds the support of preallocation (off/full) for the RBD
> > block driver.
> > If available, we use rbd_writesame() to quickly fill the image when
> > full preallocation is required.
> >
> > Signed-off-by: Stefano Garzarella <sgarz...@redhat.com>
> > ---
> > block/rbd.c | 149 ++++++++++++++++++++++++++++++++++++++-----
> > qapi/block-core.json | 4 +-
> > 2 files changed, 136 insertions(+), 17 deletions(-)
> >
> > diff --git a/block/rbd.c b/block/rbd.c
> > index 0c549c9935..29dd1bb040 100644
> > --- a/block/rbd.c
> > +++ b/block/rbd.c
> > @@ -13,6 +13,7 @@
> >
> > #include "qemu/osdep.h"
> >
> > +#include "qemu/units.h"
> > #include <rbd/librbd.h>
> > #include "qapi/error.h"
> > #include "qemu/error-report.h"
> > @@ -331,6 +332,110 @@ static void qemu_rbd_memset(RADOSCB *rcb, int64_t
> > offs)
> > }
> > }
> >
> > +static int qemu_rbd_do_truncate(rbd_image_t image, int64_t offset,
> > + PreallocMode prealloc, Error **errp)
> > +{
> > + uint64_t current_length;
> > + char *buf = NULL;
> > + int ret;
> > +
> > + ret = rbd_get_size(image, ¤t_length);
> > + if (ret < 0) {
> > + error_setg_errno(errp, -ret, "Failed to get file length");
> > + goto out;
> > + }
> > +
> > + if (current_length > offset && prealloc != PREALLOC_MODE_OFF) {
> > + error_setg(errp, "Cannot use preallocation for shrinking files");
> > + ret = -ENOTSUP;
> > + goto out;
> > + }
> > +
> > + switch (prealloc) {
> > + case PREALLOC_MODE_FULL: {
> [...]
> > + case PREALLOC_MODE_OFF:
> [...]
> > + default:
> > + error_setg(errp, "Unsupported preallocation mode: %s",
> > + PreallocMode_str(prealloc));
> > + ret = -ENOTSUP;
> > + goto out;
> > + }
>
> Other block drivers also accept only some values of PreallocMode. Okay.
>
> I wonder whether management applications need to know which values are
> supported.
Good point!
>
> Let me review support in drivers:
>
> * file (file-win32.c)
> * iscsi
> * nfs
> * qed
> * ssh
>
> - Reject all but PREALLOC_MODE_OFF
>
> * copy-on-read
> * luks (crypto.c)
> * raw
>
> - Pass through only
>
> * file host_cdrom host_device (file-posix.c)
>
> - Reject all but PREALLOC_MODE_OFF when shrinking and for non-regular
> files
> - Reject PREALLOC_MODE_FALLOC unless CONFIG_POSIX_FALLOCATE
> - Reject PREALLOC_MODE_METADATA
>
> * gluster
>
> - Reject all but PREALLOC_MODE_OFF when shrinking
> - Reject PREALLOC_MODE_FALLOC unless CONFIG_GLUSTERFS_FALLOCATE
> - Reject PREALLOC_MODE_FULL unless CONFIG_GLUSTERFS_ZEROFILL
> - Reject PREALLOC_MODE_METADATA
>
> * qcow2
>
> - Reject all but PREALLOC_MODE_OFF when shrinking and with a backing
> file
>
> * rbd with this patch
>
> - Reject all but PREALLOC_MODE_OFF when shrinking
> - Reject PREALLOC_MODE_METADATA and PREALLOC_MODE_FALLOC
>
> * sheepdog
>
> - Reject PREALLOC_MODE_METADATA and PREALLOC_MODE_FALLOC
> - Doesn't support shrinking
>
> * vdi
>
> - Reject PREALLOC_MODE_FALLOC and PREALLOC_MODE_FULL
> - Doesn't support shrinking
>
> * blkdebug
> * blklogwrites
> * blkverify
> * bochs
> * cloop
> * dmg
> * ftp
> * ftps
> * http
> * https
> * luks
> * nbd
> * null-aio
> * null-co
> * nvme
> * parallels
> * qcow
> * quorum
> * replication
> * throttle
> * vhdx
> * vmdk
> * vpc
> * vvfat
> * vxhs
>
> - These appear not to use PreallocMode: they don't implement
> .bdrv_co_truncate(), and either don't implement .bdrv_co_create() or
> implement it without a prealloc parameter.
>
> Looks good to me.
>
Thanks for the analysis!
> > +
> > + ret = 0;
> > +
> > +out:
> > + g_free(buf);
> > + return ret;
> > +}
> > +
> > static QemuOptsList runtime_opts = {
> > .name = "rbd",
> > .head = QTAILQ_HEAD_INITIALIZER(runtime_opts.head),
> [...]
> > diff --git a/qapi/block-core.json b/qapi/block-core.json
> > index 7ccbfff9d0..db25a4065b 100644
> > --- a/qapi/block-core.json
> > +++ b/qapi/block-core.json
> > @@ -4277,13 +4277,15 @@
> > # point to a snapshot.
> > # @size Size of the virtual disk in bytes
> > # @cluster-size RBD object size
> > +# @preallocation Preallocation mode (allowed values: off, full)
> > #
> > # Since: 2.12
> > ##
> > { 'struct': 'BlockdevCreateOptionsRbd',
> > 'data': { 'location': 'BlockdevOptionsRbd',
> > 'size': 'size',
> > - '*cluster-size' : 'size' } }
> > + '*cluster-size' : 'size',
> > + '*preallocation': 'PreallocMode' } }
> >
> > ##
> > # @BlockdevVmdkSubformat:
>
> The non-support of values 'metadata' and 'falloc' is not visible in
> introspection, only in documentation. No reason to block this patch, as
> the other block drivers have the same introspection weakness (only
> sheepdog and vdi bother to document).
>
> Should we address the introspection weakness? Only if there's a use for
> the information, I think.
If the management applications will use that information (or maybe also
our help pages), could be useful to have an array of 'PreallocMode'
supported per-driver.
>
> Should we improve documentation for the other block drivers?
>
Yes, e.g. for Gluster it is not updated.
If you agree, I can check and update the documentation of all drivers following
your analysis.
Cheers,
Stefano
