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Our list_sort() utility has always supported a context argument that
is passed through to the comparison routine. Now there's a use case
for the similar thing for sort().
This implements sort_r by simply extending the existing sort function
in the obvious way. To avoid code duplication, we want to implement
sort() in terms of sort_r(). The naive way to do that is
static int cmp_wrapper(const void *a, const void *b, const void *ctx)
{
int (*real_cmp)(const void*, const void*) = ctx;
return real_cmp(a, b);
}
sort(..., cmp) { sort_r(..., cmp_wrapper, cmp) }
but this would do two indirect calls for each comparison. Instead, do
as is done for the default swap functions - that only adds a cost of a
single easily predicted branch to each comparison call.
Aside from introducing support for the context argument, this also
serves as preparation for patches that will eliminate the indirect
comparison calls in common cases.
Requested-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Acked-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.