On Tue, Mar 1, 2011 at 3:02 PM, Aneesh Kumar K. V
<aneesh.ku...@linux.vnet.ibm.com> wrote:
> On Tue, 1 Mar 2011 10:22:07 +0000, Stefan Hajnoczi <stefa...@gmail.com> wrote:
>> On Tue, Mar 1, 2011 at 6:38 AM, Aneesh Kumar K.V
>> <aneesh.ku...@linux.vnet.ibm.com> wrote:
>> > Signed-off-by: Aneesh Kumar K.V <aneesh.ku...@linux.vnet.ibm.com>
>> > ---
>> > hw/9pfs/virtio-9p.c | 31 +++++++++++++++++++++++++++++++
>> > hw/9pfs/virtio-9p.h | 2 ++
>> > 2 files changed, 33 insertions(+), 0 deletions(-)
>> >
>> > diff --git a/hw/9pfs/virtio-9p.c b/hw/9pfs/virtio-9p.c
>> > index c4b0198..882f4f3 100644
>> > --- a/hw/9pfs/virtio-9p.c
>> > +++ b/hw/9pfs/virtio-9p.c
>> > @@ -1978,6 +1978,36 @@ static void v9fs_fsync(V9fsState *s, V9fsPDU *pdu)
>> > v9fs_post_do_fsync(s, pdu, err);
>> > }
>> >
>> > +static void v9fs_post_do_syncfs(V9fsState *s, V9fsPDU *pdu, int err)
>> > +{
>> > + if (err == -1) {
>> > + err = -errno;
>> > + }
>> > + complete_pdu(s, pdu, err);
>> > +}
>> > +
>> > +static void v9fs_syncfs(V9fsState *s, V9fsPDU *pdu)
>> > +{
>> > + int err;
>> > + int32_t fid;
>> > + size_t offset = 7;
>> > + V9fsFidState *fidp;
>> > +
>> > + pdu_unmarshal(pdu, offset, "d", &fid);
>> > + fidp = lookup_fid(s, fid);
>> > + if (fidp == NULL) {
>> > + err = -ENOENT;
>> > + v9fs_post_do_syncfs(s, pdu, err);
>> > + return;
>> > + }
>> > + /*
>> > + * We don't have per file system syncfs
>> > + * So just return success
>> > + */
>> > + err = 0;
>> > + v9fs_post_do_syncfs(s, pdu, err);
>> > +}
>>
>> Please explain the semantics of P9_TSYNCFS. Won't returning success
>> without doing anything lead to data integrity issues?
>
> I should actually do the 9P Operation format as commit message. Will
> add in the next update. Whether returning here would cause a data
> integrity issue, it depends what sort of guarantee we want to
> provide. So calling sync on the guest will cause all the dirty pages in
> the guest to be flushed to host. Now all those changes are in the host
> page cache and it would be nice to flush them as a part of sync but
> then since we don't have a per file system sync, the above would imply
> we flush all dirty pages on the host which can result in large
> performance impact.
You get the define the semantics of P9_TSYNCFS? I thought this is
part of a well-defined protocol :). If this is a .L extension then
it's probably a bad design and shouldn't be added to the protocol if
we can't implement it.
Is this operation supposed to flush the disk write cache too?
I think virtio-9p has a file descriptor cache. Would it be possible
to fsync() those file descriptors?
Stefan
