fs: add ksys_p{read,write}64() helpers; remove in-kernel calls to syscalls

Using the ksys_p{read,write}64() wrappers allows us to get rid of
in-kernel calls to the sys_pread64() and sys_pwrite64() syscalls.
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_p{read,write}64().

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: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>

1 files changed, 16 insertions, 4 deletions

diff --git a/fs/read_write.c b/fs/read_write.c
index fc441e1ac683..c4eabbfc90df 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -610,8 +610,8 @@ SYSCALL_DEFINE3(write, unsigned int, fd, const char __user *, buf,
         return ksys_write(fd, buf, count);
 }
 
-SYSCALL_DEFINE4(pread64, unsigned int, fd, char __user *, buf,
-                        size_t, count, loff_t, pos)
+ssize_t ksys_pread64(unsigned int fd, char __user *buf, size_t count,
+                     loff_t pos)
 {
         struct fd f;
         ssize_t ret = -EBADF;
@@ -630,8 +630,14 @@ SYSCALL_DEFINE4(pread64, unsigned int, fd, char __user *, buf,
         return ret;
 }
 
-SYSCALL_DEFINE4(pwrite64, unsigned int, fd, const char __user *, buf,
-                         size_t, count, loff_t, pos)
+SYSCALL_DEFINE4(pread64, unsigned int, fd, char __user *, buf,
+                        size_t, count, loff_t, pos)
+{
+        return ksys_pread64(fd, buf, count, pos);
+}
+
+ssize_t ksys_pwrite64(unsigned int fd, const char __user *buf,
+                      size_t count, loff_t pos)
 {
         struct fd f;
         ssize_t ret = -EBADF;
@@ -650,6 +656,12 @@ SYSCALL_DEFINE4(pwrite64, unsigned int, fd, const char __user *, buf,
         return ret;
 }
 
+SYSCALL_DEFINE4(pwrite64, unsigned int, fd, const char __user *, buf,
+                         size_t, count, loff_t, pos)
+{
+        return ksys_pwrite64(fd, buf, count, pos);
+}
+
 static ssize_t do_iter_readv_writev(struct file *filp, struct iov_iter *iter,
                 loff_t *ppos, int type, rwf_t flags)
 {