fs: add ksys_close() wrapper; remove in-kernel calls to sys_close()

Using the ksys_close() wrapper allows us to get rid of in-kernel calls
to the sys_close() 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_close(), with one subtle
difference:

The few places which checked the return value did not care about the return
value re-writing in sys_close(), so simply use a wrapper around
__close_fd().

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, 12 insertions, 0 deletions

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 41023177c8ec..38805f3447ea 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -1045,4 +1045,16 @@ static inline long ksys_ftruncate(unsigned int fd, unsigned long length)
 	return do_sys_ftruncate(fd, length, 1);
 }
 
+extern int __close_fd(struct files_struct *files, unsigned int fd);
+
+/*
+ * In contrast to sys_close(), this stub does not check whether the syscall
+ * should or should not be restarted, but returns the raw error codes from
+ * __close_fd().
+ */
+static inline int ksys_close(unsigned int fd)
+{
+	return __close_fd(current->files, fd);
+}
+
 #endif