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SubjectRe: [PATCH 00/10] iov_iter: Add new iters and use with AFS
On Thu, Sep 13, 2018 at 04:51:35PM +0100, David Howells wrote:
> Hi Al,
> Here's a set of patches that adds two new iov_iter types and then makes AFS
> use them to do I/O. The iov_iter changes are:
> (1) Separate the type from the direction in the iov_iter struct and
> provide accessor functions to wrap type checking.
> (2) Renumber the type constants to be contiguous small unsigned integers,
> starting from 0 and then use switch-statements rather than if-else
> chains using bit-testing.
> Note that the compiler can optimise this better by using CMP rather
> than AND/TEST, say, as comparing integers requires fewer CMP
> instructions or can use jump tables.
> (3) Change iov_offset from size_t to loff_t. This allows iov_offset to be
> then used as a byte offset with ITER_MAPPING and allows 4GiB and larger
> reads and writes to be proposed.
> This makes no difference on a 64-bit system, but does make a 32-bit
> compilation a bit larger.
> (4) Add an ITER_MAPPING iterator type. This provides an iterator that
> directly accesses an address_space, and assumes that the target pages
> are in some way locked (eg. PG_lock or PG_writeback).
> (5) Add an ITER_DISCARD iterator type. This provides an iterator that
> simply discards anything written to it. It cannot be used as a data
> source.

Hmm... I'll take a look in about an hour (need to finish the sodding tty-ioctl
stuff first), will post review then. Sorry, I remember seeing it posted several
weeks ago, slipped through the cracks then ;-/

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