Set cwd to '/' for the process executing insmod.

Ricardo has pointed out that under Solaris the cwd is set to '/'
during module load, while under Linux it is set to the callers cwd.
To handle this cleanly I've reworked the module *_init()/_exit()
macros so they call a *_setup()/_cleanup() function when any SPL
dependent module is loaded or unloaded.  This gives us a chance to
perform any needed modification of the process, in this case changing
the cwd.  It also handily provides a way to avoid creating wrapper
init()/exit() functions because the Solaris and Linux prototypes
differ slightly.  All dependent modules should now call the spl
helper macros spl_module_{init,exit}() instead of the native linux
versions.

Unfortunately, it appears that under Linux there has been no consistent
API in the kernel to set the cwd in a module.  Because of this I have
had to add more autoconf magic than I'd like.  However, what I have
done is correct and has been tested on RHEL5, SLES11, FC11, and CHAOS
kernels.

In addition, I have change the rootdir type from a 'void *' to the
correct 'vnode_t *' type.  And I've set rootdir to a non-NULL value.

2 files changed, 109 insertions, 3 deletions

diff --git a/module/spl/spl-generic.c b/module/spl/spl-generic.c
index 8bf97e0cf..dc0ac21d0 100644
--- a/module/spl/spl-generic.c
+++ b/module/spl/spl-generic.c
@@ -358,7 +358,8 @@ set_kallsyms_lookup_name(void)
 }
 #endif
 
-static int __init spl_init(void)
+static int
+__init spl_init(void)
 {
 	int rc = 0;
 
@@ -421,7 +422,8 @@ out1:
 	return rc;
 }
 
-static void spl_fini(void)
+static void
+spl_fini(void)
 {
 	ENTRY;
 
@@ -436,6 +438,26 @@ static void spl_fini(void)
 	debug_fini();
 }
 
+/* Called when a dependent module is loaded */
+void
+spl_setup(void)
+{
+        /*
+         * At module load time the pwd is set to '/' on a Solaris system.
+         * On a Linux system will be set to whatever directory the caller
+         * was in when executing insmod/modprobe.
+         */
+        vn_set_pwd("/");
+}
+EXPORT_SYMBOL(spl_setup);
+
+/* Called when a dependent module is unloaded */
+void
+spl_cleanup(void)
+{
+}
+EXPORT_SYMBOL(spl_cleanup);
+
 module_init(spl_init);
 module_exit(spl_fini);
 
diff --git a/module/spl/spl-vnode.c b/module/spl/spl-vnode.c
index 08c339a5a..7d2080022 100644
--- a/module/spl/spl-vnode.c
+++ b/module/spl/spl-vnode.c
@@ -34,7 +34,7 @@
 
 #define DEBUG_SUBSYSTEM S_VNODE
 
-void *rootdir = NULL;
+vnode_t *rootdir = (vnode_t *)0xabcd1234;
 EXPORT_SYMBOL(rootdir);
 
 static spl_kmem_cache_t *vn_cache;
@@ -602,6 +602,90 @@ vn_releasef(int fd)
 } /* releasef() */
 EXPORT_SYMBOL(releasef);
 
+#ifndef HAVE_SET_FS_PWD
+# ifdef HAVE_2ARGS_SET_FS_PWD
+/* Used from 2.6.25 - 2.6.31+ */
+void
+set_fs_pwd(struct fs_struct *fs, struct path *path)
+{
+        struct path old_pwd;
+
+        write_lock(&fs->lock);
+        old_pwd = fs->pwd;
+        fs->pwd = *path;
+        path_get(path);
+        write_unlock(&fs->lock);
+
+        if (old_pwd.dentry)
+                path_put(&old_pwd);
+}
+# else
+/* Used from 2.6.11 - 2.6.24 */
+void
+set_fs_pwd(struct fs_struct *fs, struct vfsmount *mnt, struct dentry *dentry)
+{
+        struct dentry *old_pwd;
+        struct vfsmount *old_pwdmnt;
+
+        write_lock(&fs->lock);
+        old_pwd = fs->pwd;
+        old_pwdmnt = fs->pwdmnt;
+        fs->pwdmnt = mntget(mnt);
+        fs->pwd = dget(dentry);
+        write_unlock(&fs->lock);
+
+        if (old_pwd) {
+                dput(old_pwd);
+                mntput(old_pwdmnt);
+        }
+}
+# endif /* HAVE_2ARGS_SET_FS_PWD */
+#endif /* HAVE_SET_FS_PWD */
+
+int
+vn_set_pwd(const char *filename)
+{
+#ifdef HAVE_2ARGS_SET_FS_PWD
+        struct path path;
+        int rc;
+        ENTRY;
+
+        rc = user_path_dir(filename, &path);
+        if (rc)
+                GOTO(out, rc);
+
+        rc = inode_permission(path.dentry->d_inode, MAY_EXEC | MAY_ACCESS);
+        if (rc)
+                GOTO(dput_and_out, rc);
+
+        set_fs_pwd(current->fs, &path);
+
+dput_and_out:
+        path_put(&path);
+#else
+        struct nameidata nd;
+        int rc;
+        ENTRY;
+
+        rc = __user_walk(filename,
+                         LOOKUP_FOLLOW|LOOKUP_DIRECTORY|LOOKUP_CHDIR, &nd);
+        if (rc)
+                GOTO(out, rc);
+
+        rc = vfs_permission(&nd, MAY_EXEC);
+        if (rc)
+                GOTO(dput_and_out, rc);
+
+        set_fs_pwd(current->fs, nd.nd_mnt, nd.nd_dentry);
+
+dput_and_out:
+        vn_path_release(&nd);
+#endif /* HAVE_2ARGS_SET_FS_PWD */
+out:
+        RETURN(-rc);
+} /* vn_set_pwd() */
+EXPORT_SYMBOL(vn_set_pwd);
+
 static int
 vn_cache_constructor(void *buf, void *cdrarg, int kmflags)
 {