kernel: add ksys_unshare() helper; remove in-kernel calls to sys_unshare()

Using this helper allows us to avoid the in-kernel calls to the
sys_unshare() 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_unshare().

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>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>

diff --git a/drivers/base/devtmpfs.c b/drivers/base/devtmpfs.c
index 3f7ee954fd2cda533de4f8d0a2f8becdda464a0b..f7768077e817b006235e3ab2602baec14b2fbaf7 100644 (file)
--- a/drivers/base/devtmpfs.c
+++ b/drivers/base/devtmpfs.c
@@ -380,7 +380,7 @@ static int devtmpfsd(void *p)
 {
        char options[] = "mode=0755";
        int *err = p;
-       *err = sys_unshare(CLONE_NEWNS);
+       *err = ksys_unshare(CLONE_NEWNS);
        if (*err)
                goto out;
        *err = ksys_mount("devtmpfs", "/", "devtmpfs", MS_SILENT, options);

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 0a9942b3e718b003994af72a6e55fe015db9d85d..e724dda509e0d822291fdcd5d1172e16fe5fc193 100644 (file)
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -961,6 +961,7 @@ int ksys_ioctl(unsigned int fd, unsigned int cmd, unsigned long arg);
 off_t ksys_lseek(unsigned int fd, off_t offset, unsigned int whence);
 ssize_t ksys_read(unsigned int fd, char __user *buf, size_t count);
 void ksys_sync(void);
+int ksys_unshare(unsigned long unshare_flags);
 
 /*
  * The following kernel syscall equivalents are just wrappers to fs-internal

diff --git a/init/do_mounts_initrd.c b/init/do_mounts_initrd.c
index 03ec0c1b75530fd7c2c84f8cd1a9b5ab162d0896..d1d3e53bdeef9d4c63933dc7b7f7608bc8ae3868 100644 (file)
--- a/init/do_mounts_initrd.c
+++ b/init/do_mounts_initrd.c
@@ -36,7 +36,7 @@ __setup("noinitrd", no_initrd);
 
 static int init_linuxrc(struct subprocess_info *info, struct cred *new)
 {
-       sys_unshare(CLONE_FS | CLONE_FILES);
+       ksys_unshare(CLONE_FS | CLONE_FILES);
        /* stdin/stdout/stderr for /linuxrc */
        ksys_open("/dev/console", O_RDWR, 0);
        ksys_dup(0);

diff --git a/kernel/fork.c b/kernel/fork.c
index b1e031aac9db7d015b044396e972d634fc22beed..f71b67dc156de26e288933525cb16dc0806056c4 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2354,7 +2354,7 @@ static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp
  * constructed. Here we are modifying the current, active,
  * task_struct.
  */
-SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
+int ksys_unshare(unsigned long unshare_flags)
 {
        struct fs_struct *fs, *new_fs = NULL;
        struct files_struct *fd, *new_fd = NULL;
@@ -2470,6 +2470,11 @@ bad_unshare_out:
        return err;
 }
 
+SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
+{
+       return ksys_unshare(unshare_flags);
+}
+
 /*
  *     Helper to unshare the files of the current task.
  *     We don't want to expose copy_files internals to