From: Eric Biggers <ebiggers@kernel.org>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: Dave Chinner <david@fromorbit.com>,
Satya Tangirala <satyat@google.com>,
linux-fscrypt@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-f2fs-devel@lists.sourceforge.net,
linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org
Subject: Re: [PATCH v4 3/7] iomap: support direct I/O with fscrypt using blk-crypto
Date: Wed, 22 Jul 2020 16:43:12 -0700 [thread overview]
Message-ID: <20200722234312.GC83434@sol.localdomain> (raw)
In-Reply-To: <20200722233247.GO3151642@magnolia>
On Wed, Jul 22, 2020 at 04:32:47PM -0700, Darrick J. Wong wrote:
> On Wed, Jul 22, 2020 at 04:26:25PM -0700, Eric Biggers wrote:
> > On Wed, Jul 22, 2020 at 03:34:04PM -0700, Eric Biggers wrote:
> > > So, something like this:
> > >
> > > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> > > index 44bad4bb8831..2816194db46c 100644
> > > --- a/fs/ext4/inode.c
> > > +++ b/fs/ext4/inode.c
> > > @@ -3437,6 +3437,15 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
> > > map.m_len = min_t(loff_t, (offset + length - 1) >> blkbits,
> > > EXT4_MAX_LOGICAL_BLOCK) - map.m_lblk + 1;
> > >
> > > + /*
> > > + * When inline encryption is enabled, sometimes I/O to an encrypted file
> > > + * has to be broken up to guarantee DUN contiguity. Handle this by
> > > + * limiting the length of the mapping returned.
> > > + */
> > > + if (!(flags & IOMAP_REPORT))
> > > + map.m_len = fscrypt_limit_io_blocks(inode, map.m_lblk,
> > > + map.m_len);
> > > +
> > > if (flags & IOMAP_WRITE)
> > > ret = ext4_iomap_alloc(inode, &map, flags);
> > > else
> > >
> > >
> > > That also avoids any confusion between pages and blocks, which is nice.
> >
> > Correction: for fiemap, ext4 actually uses ext4_iomap_begin_report() instead of
> > ext4_iomap_begin(). So we don't need to check for !IOMAP_REPORT.
> >
> > Also it could make sense to limit map.m_len after ext4_iomap_alloc() rather than
> > before, so that we don't limit the length of the extent that gets allocated but
> > rather just the length that gets returned to iomap.
>
> Naïve question here -- if the decision to truncate the bio depends on
> the file block offset, can you achieve the same thing by capping the
> length of the iovec prior to iomap_dio_rw?
>
> Granted that probably only makes sense if the LBLK IV thing is only
> supposed to be used infrequently, and having to opencode a silly loop
> might be more hassle than it's worth...
>
We *could* do the truncation there, but that would truncate the actual read() or
write(). So, userspace would see a short read or write. And I understand that
while applications are *supposed* to handle short reads and writes, many don't.
I think Dave's suggestion makes more sense, since it would make this case be
treated just like normal fragmentation of the file.
- Eric
next prev parent reply other threads:[~2020-07-22 23:43 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-20 23:37 [PATCH v4 0/7] add support for direct I/O with fscrypt using blk-crypto Satya Tangirala
2020-07-20 23:37 ` [PATCH v4 1/7] fscrypt: Add functions for direct I/O support Satya Tangirala
2020-07-22 17:04 ` Jaegeuk Kim
2020-07-20 23:37 ` [PATCH v4 2/7] direct-io: add support for fscrypt using blk-crypto Satya Tangirala
2020-07-22 17:05 ` Jaegeuk Kim
2020-07-20 23:37 ` [PATCH v4 3/7] iomap: support direct I/O with " Satya Tangirala
2020-07-22 17:06 ` Jaegeuk Kim
2020-07-22 21:16 ` Dave Chinner
2020-07-22 22:34 ` Eric Biggers
2020-07-22 22:44 ` Matthew Wilcox
2020-07-22 23:12 ` Eric Biggers
2020-07-22 23:26 ` Eric Biggers
2020-07-22 23:32 ` Darrick J. Wong
2020-07-22 23:43 ` Eric Biggers [this message]
2020-07-23 22:07 ` Dave Chinner
2020-07-23 23:03 ` Eric Biggers
2020-07-24 1:39 ` Dave Chinner
2020-07-24 3:46 ` Eric Biggers
2020-07-24 5:31 ` Dave Chinner
2020-07-24 17:41 ` Eric Biggers
2020-07-25 23:47 ` Dave Chinner
2020-07-25 23:59 ` Dave Chinner
2020-07-26 2:42 ` Eric Biggers
2020-07-27 17:16 ` Eric Biggers
2020-07-20 23:37 ` [PATCH v4 4/7] ext4: " Satya Tangirala
2020-07-22 17:07 ` Jaegeuk Kim
2020-07-20 23:37 ` [PATCH v4 5/7] f2fs: " Satya Tangirala
2020-07-21 20:11 ` Jaegeuk Kim
2020-07-20 23:37 ` [PATCH v4 6/7] fscrypt: document inline encryption support Satya Tangirala
2020-07-22 17:01 ` Jaegeuk Kim
2020-07-20 23:37 ` [PATCH v4 7/7] fscrypt: update documentation for direct I/O support Satya Tangirala
2020-07-21 0:47 ` Eric Biggers
2020-07-22 16:57 ` Jaegeuk Kim
2020-07-21 0:56 ` [PATCH v4 0/7] add support for direct I/O with fscrypt using blk-crypto Eric Biggers
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