mm: add ksys_fadvise64_64() helper; remove in-kernel call to sys_fadvise64_64()

Using the ksys_fadvise64_64() helper allows us to avoid the in-kernel
calls to the sys_fadvise64_64() 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 ksys_fadvise64_64().

Some compat stubs called sys_fadvise64(), which then just passed through
the arguments to sys_fadvise64_64(). Get rid of this indirection, and call
ksys_fadvise64_64() directly.

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, 9 insertions, 0 deletions

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 613b8127834d..466d408deefd 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -970,6 +970,15 @@ ssize_t ksys_pread64(unsigned int fd, char __user *buf, size_t count,
 ssize_t ksys_pwrite64(unsigned int fd, const char __user *buf,
 		      size_t count, loff_t pos);
 int ksys_fallocate(int fd, int mode, loff_t offset, loff_t len);
+#ifdef CONFIG_ADVISE_SYSCALLS
+int ksys_fadvise64_64(int fd, loff_t offset, loff_t len, int advice);
+#else
+static inline int ksys_fadvise64_64(int fd, loff_t offset, loff_t len,
+				    int advice)
+{
+	return -EINVAL;
+}
+#endif
 
 /*
  * The following kernel syscall equivalents are just wrappers to fs-internal