fs: add ksys_lseek() helper; remove in-kernel calls to sys_lseek()

Using this helper allows us to avoid the in-kernel calls to the
sys_lseek() 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_lseek().

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, 7 insertions, 2 deletions

diff --git a/fs/read_write.c b/fs/read_write.c
index 8e8f0b4f52e2..b38b008a078e 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -301,7 +301,7 @@ loff_t vfs_llseek(struct file *file, loff_t offset, int whence)
 }
 EXPORT_SYMBOL(vfs_llseek);
 
-SYSCALL_DEFINE3(lseek, unsigned int, fd, off_t, offset, unsigned int, whence)
+off_t ksys_lseek(unsigned int fd, off_t offset, unsigned int whence)
 {
 	off_t retval;
 	struct fd f = fdget_pos(fd);
@@ -319,10 +319,15 @@ SYSCALL_DEFINE3(lseek, unsigned int, fd, off_t, offset, unsigned int, whence)
 	return retval;
 }
 
+SYSCALL_DEFINE3(lseek, unsigned int, fd, off_t, offset, unsigned int, whence)
+{
+	return ksys_lseek(fd, offset, whence);
+}
+
 #ifdef CONFIG_COMPAT
 COMPAT_SYSCALL_DEFINE3(lseek, unsigned int, fd, compat_off_t, offset, unsigned int, whence)
 {
-	return sys_lseek(fd, offset, whence);
+	return ksys_lseek(fd, offset, whence);
 }
 #endif