From: David Laight <David.Laight@ACULAB.COM>
To: 'Christoph Hellwig' <hch@infradead.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"io-uring@vger.kernel.org" <io-uring@vger.kernel.org>,
Jens Axboe <axboe@kernel.dk>,
"David S. Miller" <davem@davemloft.net>,
Al Viro <viro@zeniv.linux.org.uk>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: RE: [PATCH 5/9 next] scsi: Use iovec_import() instead of import_iovec().
Date: Fri, 8 Jan 2021 11:13:37 +0000 [thread overview]
Message-ID: <881cc102501e4c1a93785f0906dbd650@AcuMS.aculab.com> (raw)
In-Reply-To: <20200921142204.GE24515@infradead.org>
From: Christoph Hellwig
> Sent: 21 September 2020 15:22
>
> So looking at the various callers I'm not sure this API is the
> best. If we want to do something fancy I'd hide the struct iovec
> instances entirely with something like:
>
> struct iov_storage {
> struct iovec stack[UIO_FASTIOV], *vec;
> }
>
> int iov_iter_import_iovec(struct iov_iter *iter, struct iov_storage *s,
> const struct iovec __user *vec, unsigned long nr_segs,
> int type);
>
> and then add a new helper to free the thing if needed:
>
> void iov_iter_release_iovec(struct iov_storage *s)
> {
> if (s->vec != s->stack)
> kfree(s->vec);
> }
I've been looking at this code again now most of the pending changes
are in Linus's tree.
I was actually looking at going one stage further.
The 'iov_iter' is always allocated with the 'iov_storage' *above).
Usually both are on the callers stack - possibly in different functions.
So add:
struct iovec_iter {
struct iov_iter iter;
struct iovec to_free;
struct iovec stack[UIO_FASTIOV];
};
int __iovec_import(struct iovec_iter *, const struct iovec __user *vec,
unsigned long nr_segs, int type, bool compat);
And a 'clean' function to do kfree(iovec->to_free);
This reduces the complexity of most of the callers.
I started doing the changes, but got in a mess in io_uring.c (as usual).
I think I've got a patch pending (in my brain) to simplify the io_uring code.
The plan is to add:
if (iter->iov != xxx->to_free)
iter->iov = xxx->stack;
Prior to every use of the iter.
This fixes up anything that got broken by a memcpy() of the fields.
The tidyup code is then always kfree(xxx->to_free).
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
prev parent reply other threads:[~2021-01-08 11:16 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-15 14:55 [PATCH 5/9 next] scsi: Use iovec_import() instead of import_iovec() David Laight
2020-09-21 14:22 ` Christoph Hellwig
2020-09-21 14:50 ` David Laight
2021-01-08 11:13 ` David Laight [this message]
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