From: Dominique Martinet <asmadeus@codewreck.org>
To: David Howells <dhowells@redhat.com>
Cc: Jeff Layton <jlayton@kernel.org>,
Steve French <smfrench@gmail.com>,
Matthew Wilcox <willy@infradead.org>,
Marc Dionne <marc.dionne@auristor.com>,
Paulo Alcantara <pc@manguebit.com>,
Shyam Prasad N <sprasad@microsoft.com>,
Tom Talpey <tom@talpey.com>,
Eric Van Hensbergen <ericvh@kernel.org>,
Ilya Dryomov <idryomov@gmail.com>,
Christian Brauner <christian@brauner.io>,
linux-cachefs@redhat.com, linux-afs@lists.infradead.org,
linux-cifs@vger.kernel.org, linux-nfs@vger.kernel.org,
ceph-devel@vger.kernel.org, v9fs@lists.linux.dev,
linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
Latchesar Ionkov <lucho@ionkov.net>,
Christian Schoenebeck <linux_oss@crudebyte.com>
Subject: Re: [PATCH v5 40/40] 9p: Use netfslib read/write_iter
Date: Wed, 3 Jan 2024 22:00:03 +0900 [thread overview]
Message-ID: <ZZVaU_vI90WcV_jl@codewreck.org> (raw)
In-Reply-To: <355430.1704285574@warthog.procyon.org.uk>
David Howells wrote on Wed, Jan 03, 2024 at 12:39:34PM +0000:
> > p9_client_write return value should always be subreq->len, but I believe
> > we should use it unless err is set.
> > (It's also possible for partial writes to happen, e.g. p9_client_write
> > looped a few times and then failed, at which point the size returned
> > would be the amount that actually got through -- we probably should do
> > something with that?)
>
> How about something like:
>
> - int err;
> + int err, len;
>
> trace_netfs_sreq(subreq, netfs_sreq_trace_submit);
> - p9_client_write(fid, subreq->start, &subreq->io_iter, &err);
> - netfs_write_subrequest_terminated(subreq, err < 0 ? err : subreq->len,
> - false);
> + len = p9_client_write(fid, subreq->start, &subreq->io_iter, &err);
> + netfs_write_subrequest_terminated(subreq, len ?: err, false);
I think that'll be fine; plain write() syscall works like this when an
error happens after some data has been flushed, and I assume there'll be
some retry if this happpened on something like a flush dirty and it got
a partial write reported?
> > > + if (file) {
> > > + fid = file->private_data;
> > > + BUG_ON(!fid);
> >
> > This probably should be WARN + return EINVAL like find by inode?
> > It's certainly a huge problem, but we should avoid BUG if possible...
>
> Sure. The BUG_ON() was already there, but I can turn it into a WARN+error.
Thanks.
> > nit: not sure what's cleaner?
> > Since there's a message that makes for a bit awkward if...
> >
> > if (WARN_ONCE(!fid, "folio expected an open fid inode->i_private=%p\n",
> > rreq->inode->i_private))
> > return -EINVAL;
> >
> > (as a side note, I'm not sure what to make of this i_private pointer
> > here, but if that'll help you figure something out sure..)
>
> Um. 9p is using i_private. But perhaps i_ino would be a better choice:
>
> if (file) {
> fid = file->private_data;
> if (!fid)
> goto no_fid;
> p9_fid_get(fid);
> } else {
> fid = v9fs_fid_find_inode(rreq->inode, writing, INVALID_UID, true);
> if (!fid)
> goto no_fid;
> }
>
> ...
>
> no_fid:
> WARN_ONCE(1, "folio expected an open fid inode->i_ino=%lx\n",
> rreq->inode->i_ino);
> return -EINVAL;
Might be useful to track down if this came frm a file without private
data or lookup failing, but given this was a bug I guess we can deal
with that when that happens -- ack.
> > This is as follow on your netfs-lib branch:
> > - WARN_ON(rreq->origin == NETFS_READ_FOR_WRITE &&
> > - !(fid->mode & P9_ORDWR));
> > -
> > - p9_fid_get(fid);
> > + WARN_ON(rreq->origin == NETFS_READ_FOR_WRITE && !(fid->mode & P9_ORDWR));
> >
> > So the WARN_ON has been reverted back with only indentation changed;
> > I guess there were patterns that were writing despite the fid not having
> > been open as RDWR?
> > Do you still have details about these?
>
> The condition in the WARN_ON() here got changed. It was:
>
> WARN_ON(writing && ...
>
> at one point, but that caused a bunch of incorrect warning to appear because
> only NETFS_READ_FOR_WRITE requires read-access as well as write-access. All
> the others:
>
> bool writing = (rreq->origin == NETFS_READ_FOR_WRITE ||
> rreq->origin == NETFS_WRITEBACK ||
> rreq->origin == NETFS_WRITETHROUGH ||
> rreq->origin == NETFS_LAUNDER_WRITE ||
> rreq->origin == NETFS_UNBUFFERED_WRITE ||
> rreq->origin == NETFS_DIO_WRITE);
>
> only require write-access.
Thanks for clarifying
> > If a file has been open without the write bit it might not go through,
> > and it's incredibly difficult to get such users back to userspace in
> > async cases (e.g. mmap flushes), so would like to understand that.
>
> The VFS/VM should prevent writing to files that aren't open O_WRONLY or
> O_RDWR, so I don't think we should be called in otherwise.
Historically this check was more about finding a fid that wasn't opened
properly than the VFS doing something weird (e.g. by calling mprotect
after mmap and us missing that -- would need to check if that works
actually...)
> > > + return netfs_page_mkwrite(vmf, NULL);
> >
> > (I guess there's no helper that could be used directly in .page_mkwrite
> > op?)
>
> I could provide a helper that just supplies NULL as the second argument. I
> think only 9p will use it, but that's fine.
If we're the only user I guess we shouldn't bother with it at this
point, we can come back to it if this ever becomes common.
--
Dominique Martinet | Asmadeus
next prev parent reply other threads:[~2024-01-03 13:00 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-21 13:22 [PATCH v5 00/40] netfs, afs, 9p: Delegate high-level I/O to netfslib David Howells
2023-12-21 13:22 ` [PATCH v5 01/40] afs: Remove whitespace before most ')' from the trace header David Howells
2023-12-21 13:22 ` [PATCH v5 02/40] afs: Automatically generate trace tag enums David Howells
2023-12-21 13:22 ` [PATCH v5 03/40] netfs, fscache: Move fs/fscache/* into fs/netfs/ David Howells
2023-12-21 13:22 ` [PATCH v5 04/40] netfs, fscache: Combine fscache with netfs David Howells
2023-12-21 13:23 ` [PATCH v5 05/40] netfs, fscache: Remove ->begin_cache_operation David Howells
2023-12-21 13:23 ` [PATCH v5 06/40] netfs, fscache: Move /proc/fs/fscache to /proc/fs/netfs and put in a symlink David Howells
2024-01-03 16:49 ` Marc Dionne
2023-12-21 13:23 ` [PATCH v5 07/40] netfs: Move pinning-for-writeback from fscache to netfs David Howells
2023-12-21 13:23 ` [PATCH v5 08/40] netfs: Add a procfile to list in-progress requests David Howells
2023-12-21 13:23 ` [PATCH v5 09/40] netfs: Allow the netfs to make the io (sub)request alloc larger David Howells
2023-12-21 13:23 ` [PATCH v5 10/40] netfs: Add a ->free_subrequest() op David Howells
2023-12-21 13:23 ` [PATCH v5 11/40] afs: Don't use folio->private to record partial modification David Howells
2023-12-21 13:23 ` [PATCH v5 12/40] netfs: Provide invalidate_folio and release_folio calls David Howells
2023-12-21 13:23 ` [PATCH v5 13/40] netfs: Implement unbuffered/DIO vs buffered I/O locking David Howells
2023-12-21 13:23 ` [PATCH v5 14/40] netfs: Add iov_iters to (sub)requests to describe various buffers David Howells
2023-12-21 13:23 ` [PATCH v5 15/40] netfs: Add support for DIO buffering David Howells
2023-12-26 16:54 ` Nathan Chancellor
2023-12-28 10:47 ` Christian Brauner
2023-12-28 16:58 ` Nathan Chancellor
2023-12-21 13:23 ` [PATCH v5 16/40] netfs: Provide tools to create a buffer in an xarray David Howells
2023-12-21 13:23 ` [PATCH v5 17/40] netfs: Add func to calculate pagecount/size-limited span of an iterator David Howells
2023-12-21 13:23 ` [PATCH v5 18/40] netfs: Limit subrequest by size or number of segments David Howells
2023-12-21 13:23 ` [PATCH v5 19/40] netfs: Extend the netfs_io_*request structs to handle writes David Howells
2023-12-21 13:23 ` [PATCH v5 20/40] netfs: Add a hook to allow tell the netfs to update its i_size David Howells
2023-12-21 13:23 ` [PATCH v5 21/40] netfs: Make netfs_put_request() handle a NULL pointer David Howells
2023-12-21 13:23 ` [PATCH v5 22/40] netfs: Make the refcounting of netfs_begin_read() easier to use David Howells
2023-12-21 13:23 ` [PATCH v5 23/40] netfs: Prep to use folio->private for write grouping and streaming write David Howells
2023-12-21 13:23 ` [PATCH v5 24/40] netfs: Dispatch write requests to process a writeback slice David Howells
2023-12-21 13:23 ` [PATCH v5 25/40] netfs: Provide func to copy data to pagecache for buffered write David Howells
2023-12-21 13:23 ` [PATCH v5 26/40] netfs: Make netfs_read_folio() handle streaming-write pages David Howells
2023-12-21 13:23 ` [PATCH v5 27/40] netfs: Allocate multipage folios in the writepath David Howells
2023-12-21 13:23 ` [PATCH v5 28/40] netfs: Implement unbuffered/DIO read support David Howells
2023-12-21 13:23 ` [PATCH v5 29/40] netfs: Implement unbuffered/DIO write support David Howells
2023-12-21 13:23 ` [PATCH v5 30/40] netfs: Implement buffered write API David Howells
2023-12-21 13:23 ` [PATCH v5 31/40] netfs: Allow buffered shared-writeable mmap through netfs_page_mkwrite() David Howells
2023-12-21 13:23 ` [PATCH v5 32/40] netfs: Provide netfs_file_read_iter() David Howells
2023-12-21 13:23 ` [PATCH v5 33/40] netfs, cachefiles: Pass upper bound length to allow expansion David Howells
2024-01-02 14:04 ` Gao Xiang
2024-01-02 17:11 ` David Howells
2024-01-02 20:37 ` Gao Xiang
2024-01-03 10:15 ` Jia Zhu
2023-12-21 13:23 ` [PATCH v5 34/40] netfs: Provide a writepages implementation David Howells
2023-12-21 13:23 ` [PATCH v5 35/40] netfs: Provide a launder_folio implementation David Howells
2023-12-21 13:23 ` [PATCH v5 36/40] netfs: Implement a write-through caching option David Howells
2023-12-21 13:23 ` [PATCH v5 37/40] netfs: Optimise away reads above the point at which there can be no data David Howells
2023-12-21 23:01 ` Nathan Chancellor
2023-12-22 11:49 ` David Howells
2023-12-22 12:00 ` [PATCH] Fix oops in NFS David Howells
2024-01-05 4:52 ` Matthew Wilcox
2024-01-05 10:12 ` David Howells
2024-01-05 13:17 ` Matthew Wilcox
2024-01-05 17:20 ` Dominique Martinet
2024-01-05 11:48 ` David Howells
2024-01-05 14:33 ` David Howells
2023-12-21 13:23 ` [PATCH v5 38/40] netfs: Export the netfs_sreq tracepoint David Howells
2023-12-21 13:23 ` [PATCH v5 39/40] afs: Use the netfs write helpers David Howells
2023-12-21 13:23 ` [PATCH v5 40/40] 9p: Use netfslib read/write_iter David Howells
2024-01-03 7:22 ` Dominique Martinet
2024-01-03 19:52 ` Eric Van Hensbergen
2024-01-03 12:08 ` David Howells
2024-01-03 12:39 ` David Howells
2024-01-03 13:00 ` Dominique Martinet [this message]
2024-05-09 17:15 ` Andrea Righi
2024-05-09 21:33 ` David Howells
2024-05-10 5:53 ` Andrea Righi
2024-05-10 7:57 ` David Howells
2024-05-23 7:44 ` David Howells
2023-12-22 13:02 ` [PATCH] Fix EROFS Kconfig David Howells
2023-12-23 3:55 ` Jingbo Xu
2023-12-23 13:32 ` Gao Xiang
2024-01-02 15:39 ` [PATCH v5 40/40] 9p: Use netfslib read/write_iter David Howells
2024-01-02 21:49 ` [PATCH] 9p: Fix initialisation of netfs_inode for 9p David Howells
2024-01-03 13:10 ` Dominique Martinet
2024-01-03 13:59 ` David Howells
2024-01-03 14:04 ` David Howells
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