fs: add ksys_read() helper; remove in-kernel calls to sys_read()

Using this helper allows us to avoid the in-kernel calls to the
sys_read() 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_read().

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: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>

1 files changed, 6 insertions, 1 deletions

diff --git a/fs/read_write.c b/fs/read_write.c
index b38b008a078e..fc441e1ac683 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -568,7 +568,7 @@ static inline void file_pos_write(struct file *file, loff_t pos)
 	file->f_pos = pos;
 }
 
-SYSCALL_DEFINE3(read, unsigned int, fd, char __user *, buf, size_t, count)
+ssize_t ksys_read(unsigned int fd, char __user *buf, size_t count)
 {
 	struct fd f = fdget_pos(fd);
 	ssize_t ret = -EBADF;
@@ -583,6 +583,11 @@ SYSCALL_DEFINE3(read, unsigned int, fd, char __user *, buf, size_t, count)
 	return ret;
 }
 
+SYSCALL_DEFINE3(read, unsigned int, fd, char __user *, buf, size_t, count)
+{
+	return ksys_read(fd, buf, count);
+}
+
 ssize_t ksys_write(unsigned int fd, const char __user *buf, size_t count)
 {
 	struct fd f = fdget_pos(fd);