Re: [PATCH RFC v5 05/16] fuse: make args->in_args[0] to be always the header

[Joanne Koong <joannelkoong@gmail.com>]

On Thu, Nov 14, 2024 at 1:05 PM Bernd Schubert
<bernd.schubert@fastmail.fm> wrote:
>
>
>
> On 11/14/24 21:57, Joanne Koong wrote:
> > On Thu, Nov 7, 2024 at 9:04 AM Bernd Schubert <bschubert@ddn.com> wrote:
> >>
> >> This change sets up FUSE operations to have headers in args.in_args[0],
> >> even for opcodes without an actual header. We do this to prepare for
> >> cleanly separating payload from headers in the future.
> >>
> >> For opcodes without a header, we use a zero-sized struct as a
> >> placeholder. This approach:
> >> - Keeps things consistent across all FUSE operations
> >> - Will help with payload alignment later
> >> - Avoids future issues when header sizes change
> >>
> >> Signed-off-by: Bernd Schubert <bschubert@ddn.com>
> >> ---
> >>  fs/fuse/dax.c    | 13 ++++++++-----
> >>  fs/fuse/dev.c    | 24 ++++++++++++++++++++----
> >>  fs/fuse/dir.c    | 41 +++++++++++++++++++++++++++--------------
> >>  fs/fuse/fuse_i.h |  7 +++++++
> >>  fs/fuse/xattr.c  |  9 ++++++---
> >>  5 files changed, 68 insertions(+), 26 deletions(-)
> >>
> >> diff --git a/fs/fuse/dax.c b/fs/fuse/dax.c
> >> index 12ef91d170bb3091ac35a33d2b9dc38330b00948..e459b8134ccb089f971bebf8da1f7fc5199c1271 100644
> >> --- a/fs/fuse/dax.c
> >> +++ b/fs/fuse/dax.c
> >> @@ -237,14 +237,17 @@ static int fuse_send_removemapping(struct inode *inode,
> >>         struct fuse_inode *fi = get_fuse_inode(inode);
> >>         struct fuse_mount *fm = get_fuse_mount(inode);
> >>         FUSE_ARGS(args);
> >> +       struct fuse_zero_in zero_arg;
> >>
> >>         args.opcode = FUSE_REMOVEMAPPING;
> >>         args.nodeid = fi->nodeid;
> >> -       args.in_numargs = 2;
> >> -       args.in_args[0].size = sizeof(*inargp);
> >> -       args.in_args[0].value = inargp;
> >> -       args.in_args[1].size = inargp->count * sizeof(*remove_one);
> >> -       args.in_args[1].value = remove_one;
> >> +       args.in_numargs = 3;
> >> +       args.in_args[0].size = sizeof(zero_arg);
> >> +       args.in_args[0].value = &zero_arg;
> >> +       args.in_args[1].size = sizeof(*inargp);
> >> +       args.in_args[1].value = inargp;
> >> +       args.in_args[2].size = inargp->count * sizeof(*remove_one);
> >> +       args.in_args[2].value = remove_one;
> >>         return fuse_simple_request(fm, &args);
> >>  }
> >>
> >> diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
> >> index dbc222f9b0f0e590ce3ef83077e6b4cff03cff65..6effef4073da3dad2f6140761eca98147a41d88d 100644
> >> --- a/fs/fuse/dev.c
> >> +++ b/fs/fuse/dev.c
> >> @@ -1007,6 +1007,19 @@ static int fuse_copy_args(struct fuse_copy_state *cs, unsigned numargs,
> >>
> >>         for (i = 0; !err && i < numargs; i++)  {
> >>                 struct fuse_arg *arg = &args[i];
> >> +
> >> +               /* zero headers */
> >> +               if (arg->size == 0) {
> >> +                       if (WARN_ON_ONCE(i != 0)) {
> >> +                               if (cs->req)
> >> +                                       pr_err_once(
> >> +                                               "fuse: zero size header in opcode %d\n",
> >> +                                               cs->req->in.h.opcode);
> >> +                               return -EINVAL;
> >> +                       }
> >> +                       continue;
> >> +               }
> >> +
> >>                 if (i == numargs - 1 && argpages)
> >>                         err = fuse_copy_pages(cs, arg->size, zeroing);
> >>                 else
> >> @@ -1662,6 +1675,7 @@ static int fuse_retrieve(struct fuse_mount *fm, struct inode *inode,
> >>         size_t args_size = sizeof(*ra);
> >>         struct fuse_args_pages *ap;
> >>         struct fuse_args *args;
> >> +       struct fuse_zero_in zero_arg;
> >>
> >>         offset = outarg->offset & ~PAGE_MASK;
> >>         file_size = i_size_read(inode);
> >> @@ -1688,7 +1702,7 @@ static int fuse_retrieve(struct fuse_mount *fm, struct inode *inode,
> >>         args = &ap->args;
> >>         args->nodeid = outarg->nodeid;
> >>         args->opcode = FUSE_NOTIFY_REPLY;
> >> -       args->in_numargs = 2;
> >> +       args->in_numargs = 3;
> >>         args->in_pages = true;
> >>         args->end = fuse_retrieve_end;
> >>
> >> @@ -1715,9 +1729,11 @@ static int fuse_retrieve(struct fuse_mount *fm, struct inode *inode,
> >>         }
> >>         ra->inarg.offset = outarg->offset;
> >>         ra->inarg.size = total_len;
> >> -       args->in_args[0].size = sizeof(ra->inarg);
> >> -       args->in_args[0].value = &ra->inarg;
> >> -       args->in_args[1].size = total_len;
> >> +       args->in_args[0].size = sizeof(zero_arg);
> >> +       args->in_args[0].value = &zero_arg;
> >> +       args->in_args[1].size = sizeof(ra->inarg);
> >> +       args->in_args[1].value = &ra->inarg;
> >> +       args->in_args[2].size = total_len;
> >>
> >>         err = fuse_simple_notify_reply(fm, args, outarg->notify_unique);
> >>         if (err)
> >
> > Do we also need to add a zero arg header for FUSE_READLINK,
> > FUSE_DESTROY, and FUSE_BATCH_FORGET requests as well?
> >
>
> Thanks for looking at the patch! I should have added to the commit message
> that I didn't modify these, as they don't have an in argument at all.
>

Thanks for clarifying! (and apologies for the late review. I haven't
been keeping up with these patches since RFC v3 but I'm planning to
get up to speed and take a deeper look at these tomorrow + next week).

I think the FUSE_BATCH_FORGET request does use in args, depending on
the number of forget requests.


Thanks,
Joanne
>
> Thanks,
> Bernd