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From: Amir Goldstein <amir73il@gmail.com>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	linux-nvdimm <linux-nvdimm@lists.01.org>,
	virtio-fs@redhat.com, Stefan Hajnoczi <stefanha@redhat.com>,
	"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Peng Tao <tao.peng@linux.alibaba.com>
Subject: Re: [PATCH 12/20] fuse: Introduce setupmapping/removemapping commands
Date: Wed, 11 Mar 2020 09:03:42 +0200	[thread overview]
Message-ID: <CAOQ4uxh2WdLdbcMp+qvQCX2hiBx+hLO1z5wkZtc-7GCuDdsthw@mail.gmail.com> (raw)
In-Reply-To: <20200310203321.GF38440@redhat.com>

On Tue, Mar 10, 2020 at 10:34 PM Vivek Goyal <vgoyal@redhat.com> wrote:
>
> On Tue, Mar 10, 2020 at 08:49:49PM +0100, Miklos Szeredi wrote:
> > On Wed, Mar 4, 2020 at 5:59 PM Vivek Goyal <vgoyal@redhat.com> wrote:
> > >
> > > Introduce two new fuse commands to setup/remove memory mappings. This
> > > will be used to setup/tear down file mapping in dax window.
> > >
> > > Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
> > > Signed-off-by: Peng Tao <tao.peng@linux.alibaba.com>
> > > ---
> > >  include/uapi/linux/fuse.h | 37 +++++++++++++++++++++++++++++++++++++
> > >  1 file changed, 37 insertions(+)
> > >
> > > diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
> > > index 5b85819e045f..62633555d547 100644
> > > --- a/include/uapi/linux/fuse.h
> > > +++ b/include/uapi/linux/fuse.h
> > > @@ -894,4 +894,41 @@ struct fuse_copy_file_range_in {
> > >         uint64_t        flags;
> > >  };
> > >
> > > +#define FUSE_SETUPMAPPING_ENTRIES 8
> > > +#define FUSE_SETUPMAPPING_FLAG_WRITE (1ull << 0)
> > > +struct fuse_setupmapping_in {
> > > +       /* An already open handle */
> > > +       uint64_t        fh;
> > > +       /* Offset into the file to start the mapping */
> > > +       uint64_t        foffset;
> > > +       /* Length of mapping required */
> > > +       uint64_t        len;
> > > +       /* Flags, FUSE_SETUPMAPPING_FLAG_* */
> > > +       uint64_t        flags;
> > > +       /* Offset in Memory Window */
> > > +       uint64_t        moffset;
> > > +};
> > > +
> > > +struct fuse_setupmapping_out {
> > > +       /* Offsets into the cache of mappings */
> > > +       uint64_t        coffset[FUSE_SETUPMAPPING_ENTRIES];
> > > +        /* Lengths of each mapping */
> > > +        uint64_t       len[FUSE_SETUPMAPPING_ENTRIES];
> > > +};
> >
> > fuse_setupmapping_out together with FUSE_SETUPMAPPING_ENTRIES seem to be unused.
>
> This looks like leftover from the old code. I will get rid of it. Thanks.
>

Hmm. I wonder if we should keep some out args for future extensions.
Maybe return the mapped size even though it is all or nothing at this
point?

I have interest in a similar FUSE mapping functionality that was prototyped
by Miklos and published here:
https://lore.kernel.org/linux-fsdevel/CAJfpegtjEoE7H8tayLaQHG9fRSBiVuaspnmPr2oQiOZXVB1+7g@mail.gmail.com/

In this prototype, a FUSE_MAP command is used by the server to map a
range of file to the kernel for io. The command in args are quite similar to
those in fuse_setupmapping_in, but since the server is on the same host,
the mapping response is {mapfd, offset, size}.

I wonder, if we decide to go forward with this prototype (and I may well decide
to drive this forward), should the new command be overloading
FUSE_SETUPMAPPING, by using new flags or should it be a new
command? In either case, I think it would be best to try and make a decision
now in order to avoid ambiguity with protocol command/flag names later on.

If we decide that those are completely different beasts and it is agreed that
the future command will be named, for example, FUSE_SETUPIOMAP
with different arguments and that this naming will not create confusion and
ambiguity with FUSE_SETUPMAPPING, then there is no actionable item at
this time.

But it is possible that there is something to gain from using the same
command(?) and same book keeping mechanism for both types of
mappings. Even server on same host could decide that it wants
to map some file regions via mmap and some via iomap.
In that case, perhaps we should make the FUSE_SETUPMAPPING
response args expressive enough to be able to express an iomap
mapping in the future and perhaps dax code should explicitly request
for FUSE_SETUPMAPPING_FLAG_DAX mapping type?

Thoughts?

Amir.
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  reply	other threads:[~2020-03-11  7:03 UTC|newest]

Thread overview: 67+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-04 16:58 [PATCH 00/20] virtiofs: Add DAX support Vivek Goyal
2020-03-04 16:58 ` [PATCH 01/20] dax: Modify bdev_dax_pgoff() to handle NULL bdev Vivek Goyal
2020-03-04 16:58 ` [PATCH 02/20] dax: Create a range version of dax_layout_busy_page() Vivek Goyal
2020-03-10 15:19   ` Ira Weiny
2020-03-10 20:29     ` Vivek Goyal
2020-03-04 16:58 ` [PATCH 03/20] virtio: Add get_shm_region method Vivek Goyal
2020-03-10 10:53   ` Stefan Hajnoczi
2020-03-04 16:58 ` [PATCH 04/20] virtio: Implement get_shm_region for PCI transport Vivek Goyal
2020-03-10 11:04   ` Stefan Hajnoczi
2020-03-10 18:19     ` Vivek Goyal
2020-03-11 17:34       ` Stefan Hajnoczi
2020-03-11 19:29         ` Vivek Goyal
2020-03-10 11:12   ` Michael S. Tsirkin
2020-03-10 18:47     ` Vivek Goyal
2020-03-10 21:27       ` Michael S. Tsirkin
2020-03-04 16:58 ` [PATCH 05/20] virtio: Implement get_shm_region for MMIO transport Vivek Goyal
2020-03-10 11:06   ` Stefan Hajnoczi
2020-03-04 16:58 ` [PATCH 06/20] virtiofs: Provide a helper function for virtqueue initialization Vivek Goyal
2020-03-10 14:10   ` Miklos Szeredi
2020-03-04 16:58 ` [PATCH 07/20] fuse: Get rid of no_mount_options Vivek Goyal
2020-03-10 14:12   ` Miklos Szeredi
2020-03-04 16:58 ` [PATCH 08/20] fuse,virtiofs: Add a mount option to enable dax Vivek Goyal
2020-03-10 14:16   ` Miklos Szeredi
2020-03-04 16:58 ` [PATCH 09/20] virtio_fs, dax: Set up virtio_fs dax_device Vivek Goyal
2020-03-04 16:58 ` [PATCH 10/20] fuse,virtiofs: Keep a list of free dax memory ranges Vivek Goyal
2020-03-10 19:29   ` Miklos Szeredi
2020-03-04 16:58 ` [PATCH 11/20] fuse: implement FUSE_INIT map_alignment field Vivek Goyal
2020-03-10 19:31   ` Miklos Szeredi
2020-03-04 16:58 ` [PATCH 12/20] fuse: Introduce setupmapping/removemapping commands Vivek Goyal
2020-03-10 19:49   ` Miklos Szeredi
2020-03-10 20:33     ` Vivek Goyal
2020-03-11  7:03       ` Amir Goldstein [this message]
2020-03-11 14:19         ` Miklos Szeredi
2020-03-11 14:41           ` Vivek Goyal
2020-03-11 15:12             ` Miklos Szeredi
2020-03-04 16:58 ` [PATCH 13/20] fuse, dax: Implement dax read/write operations Vivek Goyal
2020-03-12  9:43   ` Miklos Szeredi
2020-03-12 16:02     ` Vivek Goyal
2020-03-13 10:18       ` Miklos Szeredi
2020-03-13 13:41         ` Vivek Goyal
2020-04-04  0:25   ` Liu Bo
2020-04-14 12:54     ` Vivek Goyal
2020-03-04 16:58 ` [PATCH 14/20] fuse,dax: add DAX mmap support Vivek Goyal
2020-03-04 16:58 ` [PATCH 15/20] fuse, dax: Take ->i_mmap_sem lock during dax page fault Vivek Goyal
2020-03-04 16:58 ` [PATCH 16/20] fuse,virtiofs: Define dax address space operations Vivek Goyal
2020-03-04 16:58 ` [PATCH 17/20] fuse,virtiofs: Maintain a list of busy elements Vivek Goyal
2020-03-04 16:58 ` [PATCH 18/20] fuse: Release file in process context Vivek Goyal
2020-03-04 16:58 ` [PATCH 19/20] fuse: Take inode lock for dax inode truncation Vivek Goyal
2020-03-04 16:58 ` [PATCH 20/20] fuse,virtiofs: Add logic to free up a memory range Vivek Goyal
2020-03-11  5:16   ` Liu Bo
2020-03-11 12:59     ` Vivek Goyal
2020-03-11 17:24       ` Liu Bo
2020-03-26  0:09   ` Liu Bo
2020-03-27 14:01     ` Vivek Goyal
2020-03-27 22:06       ` Liu Bo
2020-04-14 19:30         ` Vivek Goyal
2020-04-15 17:22           ` Liu Bo
2020-04-16 19:05             ` Vivek Goyal
2020-04-17 18:05               ` Liu Bo
2020-03-11  5:22 ` [PATCH 00/20] virtiofs: Add DAX support Amir Goldstein
2020-03-11 13:09   ` Vivek Goyal
2020-03-11 18:48   ` Vivek Goyal
2020-03-11 19:32     ` Amir Goldstein
2020-03-11 19:39       ` Vivek Goyal
2020-03-11 13:38 ` Patrick Ohly
2020-03-16 13:02   ` Vivek Goyal
2020-03-17  8:28     ` Patrick Ohly

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