| Message ID | 20190910154110.6905-3-pl@kamp.de |
|---|---|
| State | New |
| Headers | show |
| Series | add support for nfs_umount | expand |
On 10.09.19 17:41, Peter Lieven wrote: > libnfs recently added support for unmounting. Add support > in Qemu too. > > Signed-off-by: Peter Lieven <pl@kamp.de> > --- > block/nfs.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/block/nfs.c b/block/nfs.c > index 2c98508275..f39acfdb28 100644 > --- a/block/nfs.c > +++ b/block/nfs.c > @@ -398,6 +398,9 @@ static void nfs_client_close(NFSClient *client) > nfs_close(client->context, client->fh); > client->fh = NULL; > } > +#ifdef LIBNFS_FEATURE_UMOUNT > + nfs_umount(client->context); > +#endif > nfs_destroy_context(client->context); > client->context = NULL; > } I don’t understand what unmounting means in this context. Is it just generic clean-up for NFSv3 (it appears that it’s a no-op for NFSv4)? Why isn’t that done by nfs_destroy_context()? Max
Am 11.09.19 um 09:48 schrieb Max Reitz: > On 10.09.19 17:41, Peter Lieven wrote: >> libnfs recently added support for unmounting. Add support >> in Qemu too. >> >> Signed-off-by: Peter Lieven <pl@kamp.de> >> --- >> block/nfs.c | 3 +++ >> 1 file changed, 3 insertions(+) >> >> diff --git a/block/nfs.c b/block/nfs.c >> index 2c98508275..f39acfdb28 100644 >> --- a/block/nfs.c >> +++ b/block/nfs.c >> @@ -398,6 +398,9 @@ static void nfs_client_close(NFSClient *client) >> nfs_close(client->context, client->fh); >> client->fh = NULL; >> } >> +#ifdef LIBNFS_FEATURE_UMOUNT >> + nfs_umount(client->context); >> +#endif >> nfs_destroy_context(client->context); >> client->context = NULL; >> } > I don’t understand what unmounting means in this context. Is it just > generic clean-up for NFSv3 (it appears that it’s a no-op for NFSv4)? Its a call to the mount daemon on the NFSv3 server. It will effectively cause that the connection is no longer listed when showmounts -a is issued on the server. > Why isn’t that done by nfs_destroy_context()? That would have been the right place, but libnfs added support for this call only recently. I think with version 4.0.0 Peter
On Wed, Sep 11, 2019 at 5:48 PM Max Reitz <mreitz@redhat.com> wrote: > > On 10.09.19 17:41, Peter Lieven wrote: > > libnfs recently added support for unmounting. Add support > > in Qemu too. > > > > Signed-off-by: Peter Lieven <pl@kamp.de> > > --- > > block/nfs.c | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/block/nfs.c b/block/nfs.c > > index 2c98508275..f39acfdb28 100644 > > --- a/block/nfs.c > > +++ b/block/nfs.c > > @@ -398,6 +398,9 @@ static void nfs_client_close(NFSClient *client) > > nfs_close(client->context, client->fh); > > client->fh = NULL; > > } > > +#ifdef LIBNFS_FEATURE_UMOUNT > > + nfs_umount(client->context); > > +#endif > > nfs_destroy_context(client->context); > > client->context = NULL; > > } > > I don’t understand what unmounting means in this context. Is it just > generic clean-up for NFSv3 (it appears that it’s a no-op for NFSv4)? > Why isn’t that done by nfs_destroy_context()? Umount is weird since there isn't actually any state in NFSv3 and "mounting" in nfsv3 is really just a matter of converting the path to be mounted into a filehandle. That is all the mount protocol is really used for. This is all handled in a separate protocol/server called rpc.mountd that is separate from NFSd. Running as a different process and listening to a different port. And the only purpose of rpc.mountd is to take a path to a share and return a nfsv3 filehandle to the root of that path. As a side-effect, rpc.mountd also keeps track of which clients have called MNT but not yet UMNT and thus showmount -a can give a lost of all client that have "mounted" the share but not yet called "UMNT". It has no effect at all on NFSv3 and is purely cosmetic. This ONLY affects "showmount -a" output. NFSv4 does away with all these separate protocols such as mount, statd, nlm and even portmapper so there is not even a concept of showmount -a for nfsv4. As the libnfs maintainer, why did I do nfs_umount() the way I did? First of all, I think of nfs UMNT as really just cosmetic and didn't want to put too much work into it. But people wanted it. I implemented it as a sync function since I think few people would actually use it at all and it meant that I just didn't have to invest in having to build an async piupelinje. I did NOT implement it inside nfs_destroy_context() since that function is supposed to be, in my view, non-blocking andn should just tear the connection and immediately return. As unmount would be * close the tcp socket to the nfs server * open new socket to portmapper and ask "where is rpc.mountd" * close socket to portmapper, then open new socket to rpc.mountd * tell rpc.mountd to remove us from the showmount -a list * close socket I just took the cheap and easy path. Do it as a sync function with my own eventloop. Again, UMNT has no real effect on anything related to NFS except what showmount -a will return. That is one big reason why I was just not much motivated enough to build it as an async function. Once we all switch to NFSv4 this will all be moot since the MOUNT protocol no longer exists and neither does rpc.mountd. > > Max >
On 13.09.19 12:09, ronnie sahlberg wrote: > On Wed, Sep 11, 2019 at 5:48 PM Max Reitz <mreitz@redhat.com> wrote: >> >> On 10.09.19 17:41, Peter Lieven wrote: >>> libnfs recently added support for unmounting. Add support >>> in Qemu too. >>> >>> Signed-off-by: Peter Lieven <pl@kamp.de> >>> --- >>> block/nfs.c | 3 +++ >>> 1 file changed, 3 insertions(+) >>> >>> diff --git a/block/nfs.c b/block/nfs.c >>> index 2c98508275..f39acfdb28 100644 >>> --- a/block/nfs.c >>> +++ b/block/nfs.c >>> @@ -398,6 +398,9 @@ static void nfs_client_close(NFSClient *client) >>> nfs_close(client->context, client->fh); >>> client->fh = NULL; >>> } >>> +#ifdef LIBNFS_FEATURE_UMOUNT >>> + nfs_umount(client->context); >>> +#endif >>> nfs_destroy_context(client->context); >>> client->context = NULL; >>> } >> >> I don’t understand what unmounting means in this context. Is it just >> generic clean-up for NFSv3 (it appears that it’s a no-op for NFSv4)? >> Why isn’t that done by nfs_destroy_context()? > > Umount is weird since there isn't actually any state in NFSv3 and > "mounting" in nfsv3 is really just a matter of converting the path to > be mounted into a filehandle. > That is all the mount protocol is really used for. > > This is all handled in a separate protocol/server called rpc.mountd > that is separate from NFSd. Running as a different process and > listening to a different port. > And the only purpose of rpc.mountd is to take a path to a share and > return a nfsv3 filehandle to the root of that path. > As a side-effect, rpc.mountd also keeps track of which clients have > called MNT but not yet UMNT and thus showmount -a > can give a lost of all client that have "mounted" the share but not > yet called "UMNT". > > It has no effect at all on NFSv3 and is purely cosmetic. This ONLY > affects "showmount -a" output. > NFSv4 does away with all these separate protocols such as mount, > statd, nlm and even portmapper > so there is not even a concept of showmount -a for nfsv4. > > > As the libnfs maintainer, why did I do nfs_umount() the way I did? > First of all, I think of nfs UMNT as really just cosmetic and didn't > want to put too much work into it. But people wanted it. > > I implemented it as a sync function since I think few people would > actually use it at all and it meant that I just didn't have to invest > in having to build an async piupelinje. > > I did NOT implement it inside nfs_destroy_context() since that > function is supposed to be, in my view, non-blocking andn should just > tear the connection and immediately return. > As unmount would be > * close the tcp socket to the nfs server > * open new socket to portmapper and ask "where is rpc.mountd" > * close socket to portmapper, then open new socket to rpc.mountd > * tell rpc.mountd to remove us from the showmount -a list > * close socket > > I just took the cheap and easy path. Do it as a sync function with my > own eventloop. > > Again, UMNT has no real effect on anything related to NFS except what > showmount -a will return. That is one big reason why > I was just not much motivated enough to build it as an async function. > > Once we all switch to NFSv4 this will all be moot since the MOUNT > protocol no longer exists and neither does rpc.mountd. OK. Thanks a lot for the detailed explanation! :-) Max
diff --git a/block/nfs.c b/block/nfs.c index 2c98508275..f39acfdb28 100644 --- a/block/nfs.c +++ b/block/nfs.c @@ -398,6 +398,9 @@ static void nfs_client_close(NFSClient *client) nfs_close(client->context, client->fh); client->fh = NULL; } +#ifdef LIBNFS_FEATURE_UMOUNT + nfs_umount(client->context); +#endif nfs_destroy_context(client->context); client->context = NULL; }
libnfs recently added support for unmounting. Add support in Qemu too. Signed-off-by: Peter Lieven <pl@kamp.de> --- block/nfs.c | 3 +++ 1 file changed, 3 insertions(+)