mm: add ksys_readahead() helper; remove in-kernel calls to sys_readahead()

Using this helper allows us to avoid the in-kernel calls to the
sys_readahead() syscall. The ksys_ prefix denotes that this function is
meant as a drop-in replacement for the syscall. In particular, it uses the
same calling convention as sys_readahead().

This patch is part of a series which removes in-kernel calls to syscalls.
On this basis, the syscall entry path can be streamlined. For details, see
http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.net

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>

1 files changed, 6 insertions, 1 deletions

diff --git a/mm/readahead.c b/mm/readahead.c
index c4ca70239233..4d57b4644f98 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -573,7 +573,7 @@ do_readahead(struct address_space *mapping, struct file *filp,
 	return force_page_cache_readahead(mapping, filp, index, nr);
 }
 
-SYSCALL_DEFINE3(readahead, int, fd, loff_t, offset, size_t, count)
+ssize_t ksys_readahead(int fd, loff_t offset, size_t count)
 {
 	ssize_t ret;
 	struct fd f;
@@ -592,3 +592,8 @@ SYSCALL_DEFINE3(readahead, int, fd, loff_t, offset, size_t, count)
 	}
 	return ret;
 }
+
+SYSCALL_DEFINE3(readahead, int, fd, loff_t, offset, size_t, count)
+{
+	return ksys_readahead(fd, offset, count);
+}