Remove vn_set_fs_pwd()/vn_set_pwd() (no need to be at / during insmod)

Per suggestion from @behlendorf in #8777, remove vn_set_fs_pwd() and
vn_set_pwd() which are only used in zfs_ioctl.c:_init() while loading
zfs.ko.

The rest of initialization functions being called here after cwd set
to / don't depend on cwd of the process except for spa_config_load().
spa_config_load() uses a relative path ".//etc/zfs/zpool.cache" when
`rootdir` is non-NULL, which is "/etc/zfs/zpool.cache" given cwd is /,
so just unconditionally use the absolute path without "./", so that
`vn_set_pwd("/")` as well as the entire functions can be removed.
This is also what FreeBSD does.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Tomohiro Kusumi <kusumi.tomohiro@osnexus.com>
Closes #8826

config/kernel-spinlock.m4

@@ -1,24 +0,0 @@
-dnl #
-dnl # 2.6.36 API change,
-dnl # The 'struct fs_struct->lock' was changed from a rwlock_t to
-dnl # a spinlock_t to improve the fastpath performance.
-dnl #
-AC_DEFUN([ZFS_AC_KERNEL_FS_STRUCT_SPINLOCK], [
-	AC_MSG_CHECKING([whether struct fs_struct uses spinlock_t])
-	tmp_flags="$EXTRA_KCFLAGS"
-	EXTRA_KCFLAGS="-Werror"
-	ZFS_LINUX_TRY_COMPILE([
-		#include <linux/sched.h>
-		#include <linux/fs_struct.h>
-	],[
-		static struct fs_struct fs;
-		spin_lock_init(&fs.lock);
-	],[
-		AC_MSG_RESULT(yes)
-		AC_DEFINE(HAVE_FS_STRUCT_SPINLOCK, 1,
-		          [struct fs_struct uses spinlock_t])
-	],[
-		AC_MSG_RESULT(no)
-	])
-	EXTRA_KCFLAGS="$tmp_flags"
-])

config/kernel.m4

@@ -12,7 +12,6 @@ AC_DEFUN([ZFS_AC_CONFIG_KERNEL], [
 	ZFS_AC_KERNEL_CTL_NAME
 	ZFS_AC_KERNEL_PDE_DATA
 	ZFS_AC_KERNEL_2ARGS_VFS_FSYNC
-	ZFS_AC_KERNEL_FS_STRUCT_SPINLOCK
 	ZFS_AC_KERNEL_KUIDGID_T
 	ZFS_AC_KERNEL_FALLOCATE
 	ZFS_AC_KERNEL_2ARGS_ZLIB_DEFLATE_WORKSPACESIZE

include/spl/sys/vnode.h

@@ -182,7 +182,6 @@ extern int vn_space(vnode_t *vp, int cmd, struct flock *bfp, int flag,
 extern file_t *vn_getf(int fd);
 extern void vn_releasef(int fd);
 extern void vn_areleasef(int fd, uf_info_t *fip);
-extern int vn_set_pwd(const char *filename);
 
 int spl_vn_init(void);
 void spl_vn_fini(void);

module/spl/spl-vnode.c

@@ -641,64 +641,6 @@ vn_areleasef(int fd, uf_info_t *fip)
 } /* releasef() */
 EXPORT_SYMBOL(areleasef);
 
-
-static void
-vn_set_fs_pwd(struct fs_struct *fs, struct path *path)
-{
-	struct path old_pwd;
-
-#ifdef HAVE_FS_STRUCT_SPINLOCK
-	spin_lock(&fs->lock);
-	old_pwd = fs->pwd;
-	fs->pwd = *path;
-	path_get(path);
-	spin_unlock(&fs->lock);
-#else
-	write_lock(&fs->lock);
-	old_pwd = fs->pwd;
-	fs->pwd = *path;
-	path_get(path);
-	write_unlock(&fs->lock);
-#endif /* HAVE_FS_STRUCT_SPINLOCK */
-
-	if (old_pwd.dentry)
-		path_put(&old_pwd);
-}
-
-int
-vn_set_pwd(const char *filename)
-{
-	struct path path;
-	mm_segment_t saved_fs;
-	int rc;
-
-	/*
-	 * user_path_dir() and __user_walk() both expect 'filename' to be
-	 * a user space address so we must briefly increase the data segment
-	 * size to ensure strncpy_from_user() does not fail with -EFAULT.
-	 */
-	saved_fs = get_fs();
-	set_fs(KERNEL_DS);
-
-	rc = user_path_dir(filename, &path);
-	if (rc)
-		goto out;
-
-	rc = inode_permission(path.dentry->d_inode, MAY_EXEC | MAY_ACCESS);
-	if (rc)
-		goto dput_and_out;
-
-	vn_set_fs_pwd(current->fs, &path);
-
-dput_and_out:
-	path_put(&path);
-out:
-	set_fs(saved_fs);
-
-	return (-rc);
-} /* vn_set_pwd() */
-EXPORT_SYMBOL(vn_set_pwd);
-
 static int
 vn_cache_constructor(void *buf, void *cdrarg, int kmflags)
 {

module/zfs/spa_config.c

@@ -93,8 +93,7 @@ spa_config_load(void)
 	 */
 	pathname = kmem_alloc(MAXPATHLEN, KM_SLEEP);
 
-	(void) snprintf(pathname, MAXPATHLEN, "%s%s",
-	    (rootdir != NULL) ? "./" : "", spa_config_path);
+	(void) snprintf(pathname, MAXPATHLEN, "%s", spa_config_path);
 
 	file = kobj_open_file(pathname);
 

module/zfs/zfs_ioctl.c

@@ -7380,13 +7380,6 @@ _init(void)
 {
 	int error;
 
-	error = -vn_set_pwd("/");
-	if (error) {
-		printk(KERN_NOTICE
-		    "ZFS: Warning unable to set pwd to '/': %d\n", error);
-		return (error);
-	}
-
 	if ((error = -zvol_init()) != 0)
 		return (error);