Take fs_struct handling to new file (fs/fs_struct.c)

Pure code move; two new helper functions for nfsd and daemonize
(unshare_fs_struct() and daemonize_fs_struct() resp.; for now -
the same code as used to be in callers).  unshare_fs_struct()
exported (for nfsd, as copy_fs_struct()/exit_fs() used to be),
copy_fs_struct() and exit_fs() don't need exports anymore.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/Makefile

@@ -11,7 +11,7 @@ obj-y :=	open.o read_write.o file_table.o super.o \
 		attr.o bad_inode.o file.o filesystems.o namespace.o \
 		seq_file.o xattr.o libfs.o fs-writeback.o \
 		pnode.o drop_caches.o splice.o sync.o utimes.o \
-		stack.o
+		stack.o fs_struct.o
 
 ifeq ($(CONFIG_BLOCK),y)
 obj-y +=	buffer.o bio.o block_dev.o direct-io.o mpage.o ioprio.o

fs/fs_struct.c

+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/fs.h>
+#include <linux/path.h>
+#include <linux/slab.h>
+
+/*
+ * Replace the fs->{rootmnt,root} with {mnt,dentry}. Put the old values.
+ * It can block.
+ */
+void set_fs_root(struct fs_struct *fs, struct path *path)
+{
+	struct path old_root;
+
+	write_lock(&fs->lock);
+	old_root = fs->root;
+	fs->root = *path;
+	path_get(path);
+	write_unlock(&fs->lock);
+	if (old_root.dentry)
+		path_put(&old_root);
+}
+
+/*
+ * Replace the fs->{pwdmnt,pwd} with {mnt,dentry}. Put the old values.
+ * It can block.
+ */
+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);
+}
+
+void chroot_fs_refs(struct path *old_root, struct path *new_root)
+{
+	struct task_struct *g, *p;
+	struct fs_struct *fs;
+	int count = 0;
+
+	read_lock(&tasklist_lock);
+	do_each_thread(g, p) {
+		task_lock(p);
+		fs = p->fs;
+		if (fs) {
+			write_lock(&fs->lock);
+			if (fs->root.dentry == old_root->dentry
+			    && fs->root.mnt == old_root->mnt) {
+				path_get(new_root);
+				fs->root = *new_root;
+				count++;
+			}
+			if (fs->pwd.dentry == old_root->dentry
+			    && fs->pwd.mnt == old_root->mnt) {
+				path_get(new_root);
+				fs->pwd = *new_root;
+				count++;
+			}
+			write_unlock(&fs->lock);
+		}
+		task_unlock(p);
+	} while_each_thread(g, p);
+	read_unlock(&tasklist_lock);
+	while (count--)
+		path_put(old_root);
+}
+
+void put_fs_struct(struct fs_struct *fs)
+{
+	/* No need to hold fs->lock if we are killing it */
+	if (atomic_dec_and_test(&fs->count)) {
+		path_put(&fs->root);
+		path_put(&fs->pwd);
+		kmem_cache_free(fs_cachep, fs);
+	}
+}
+
+void exit_fs(struct task_struct *tsk)
+{
+	struct fs_struct * fs = tsk->fs;
+
+	if (fs) {
+		task_lock(tsk);
+		tsk->fs = NULL;
+		task_unlock(tsk);
+		put_fs_struct(fs);
+	}
+}
+
+struct fs_struct *copy_fs_struct(struct fs_struct *old)
+{
+	struct fs_struct *fs = kmem_cache_alloc(fs_cachep, GFP_KERNEL);
+	/* We don't need to lock fs - think why ;-) */
+	if (fs) {
+		atomic_set(&fs->count, 1);
+		rwlock_init(&fs->lock);
+		fs->umask = old->umask;
+		read_lock(&old->lock);
+		fs->root = old->root;
+		path_get(&old->root);
+		fs->pwd = old->pwd;
+		path_get(&old->pwd);
+		read_unlock(&old->lock);
+	}
+	return fs;
+}
+
+int unshare_fs_struct(void)
+{
+	struct fs_struct *fsp = copy_fs_struct(current->fs);
+	if (!fsp)
+		return -ENOMEM;
+	exit_fs(current);
+	current->fs = fsp;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(unshare_fs_struct);
+
+/* to be mentioned only in INIT_TASK */
+struct fs_struct init_fs = {
+	.count		= ATOMIC_INIT(1),
+	.lock		= __RW_LOCK_UNLOCKED(init_fs.lock),
+	.umask		= 0022,
+};
+
+void daemonize_fs_struct(void)
+{
+	struct fs_struct *fs;
+
+	exit_fs(current);	/* current->fs->count--; */
+	fs = &init_fs;
+	current->fs = fs;
+	atomic_inc(&fs->count);
+}

fs/internal.h

@@ -11,6 +11,7 @@
 
 struct super_block;
 struct linux_binprm;
+struct path;
 
 /*
  * block_dev.c
@@ -60,3 +61,8 @@ extern void umount_tree(struct vfsmount *, int, struct list_head *);
 extern struct vfsmount *copy_tree(struct vfsmount *, struct dentry *, int);
 
 extern void __init mnt_init(void);
+
+/*
+ * fs_struct.c
+ */
+extern void chroot_fs_refs(struct path *, struct path *);

fs/namei.c

@@ -2897,10 +2897,3 @@ EXPORT_SYMBOL(vfs_symlink);
 EXPORT_SYMBOL(vfs_unlink);
 EXPORT_SYMBOL(dentry_unhash);
 EXPORT_SYMBOL(generic_readlink);
-
-/* to be mentioned only in INIT_TASK */
-struct fs_struct init_fs = {
-	.count		= ATOMIC_INIT(1),
-	.lock		= __RW_LOCK_UNLOCKED(init_fs.lock),
-	.umask		= 0022,
-};

fs/namespace.c

@@ -2092,74 +2092,6 @@ SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
 	return retval;
 }
 
-/*
- * Replace the fs->{rootmnt,root} with {mnt,dentry}. Put the old values.
- * It can block. Requires the big lock held.
- */
-void set_fs_root(struct fs_struct *fs, struct path *path)
-{
-	struct path old_root;
-
-	write_lock(&fs->lock);
-	old_root = fs->root;
-	fs->root = *path;
-	path_get(path);
-	write_unlock(&fs->lock);
-	if (old_root.dentry)
-		path_put(&old_root);
-}
-
-/*
- * Replace the fs->{pwdmnt,pwd} with {mnt,dentry}. Put the old values.
- * It can block. Requires the big lock held.
- */
-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);
-}
-
-static void chroot_fs_refs(struct path *old_root, struct path *new_root)
-{
-	struct task_struct *g, *p;
-	struct fs_struct *fs;
-	int count = 0;
-
-	read_lock(&tasklist_lock);
-	do_each_thread(g, p) {
-		task_lock(p);
-		fs = p->fs;
-		if (fs) {
-			write_lock(&fs->lock);
-			if (fs->root.dentry == old_root->dentry
-			    && fs->root.mnt == old_root->mnt) {
-				path_get(new_root);
-				fs->root = *new_root;
-				count++;
-			}
-			if (fs->pwd.dentry == old_root->dentry
-			    && fs->pwd.mnt == old_root->mnt) {
-				path_get(new_root);
-				fs->pwd = *new_root;
-				count++;
-			}
-			write_unlock(&fs->lock);
-		}
-		task_unlock(p);
-	} while_each_thread(g, p);
-	read_unlock(&tasklist_lock);
-	while (count--)
-		path_put(old_root);
-}
-
 /*
  * pivot_root Semantics:
  * Moves the root file system of the current process to the directory put_old,

fs/nfsd/nfssvc.c

@@ -404,7 +404,6 @@ static int
 nfsd(void *vrqstp)
 {
 	struct svc_rqst *rqstp = (struct svc_rqst *) vrqstp;
-	struct fs_struct *fsp;
 	int err, preverr = 0;
 
 	/* Lock module and set up kernel thread */
@@ -413,13 +412,11 @@ nfsd(void *vrqstp)
 	/* At this point, the thread shares current->fs
 	 * with the init process. We need to create files with a
 	 * umask of 0 instead of init's umask. */
-	fsp = copy_fs_struct(current->fs);
-	if (!fsp) {
+	if (unshare_fs_struct() < 0) {
 		printk("Unable to start nfsd thread: out of memory\n");
 		goto out;
 	}
-	exit_fs(current);
-	current->fs = fsp;
+
 	current->fs->umask = 0;
 
 	/*

include/linux/fs_struct.h

@@ -20,5 +20,7 @@ extern void set_fs_root(struct fs_struct *, struct path *);
 extern void set_fs_pwd(struct fs_struct *, struct path *);
 extern struct fs_struct *copy_fs_struct(struct fs_struct *);
 extern void put_fs_struct(struct fs_struct *);
+extern void daemonize_fs_struct(void);
+extern int unshare_fs_struct(void);
 
 #endif /* _LINUX_FS_STRUCT_H */

kernel/exit.c

@@ -429,7 +429,6 @@ EXPORT_SYMBOL(disallow_signal);
 void daemonize(const char *name, ...)
 {
 	va_list args;
-	struct fs_struct *fs;
 	sigset_t blocked;
 
 	va_start(args, name);
@@ -462,11 +461,7 @@ void daemonize(const char *name, ...)
 
 	/* Become as one with the init task */
 
-	exit_fs(current);	/* current->fs->count--; */
-	fs = init_task.fs;
-	current->fs = fs;
-	atomic_inc(&fs->count);
-
+	daemonize_fs_struct();
 	exit_files(current);
 	current->files = init_task.files;
 	atomic_inc(&current->files->count);
@@ -565,30 +560,6 @@ void exit_files(struct task_struct *tsk)
 	}
 }
 
-void put_fs_struct(struct fs_struct *fs)
-{
-	/* No need to hold fs->lock if we are killing it */
-	if (atomic_dec_and_test(&fs->count)) {
-		path_put(&fs->root);
-		path_put(&fs->pwd);
-		kmem_cache_free(fs_cachep, fs);
-	}
-}
-
-void exit_fs(struct task_struct *tsk)
-{
-	struct fs_struct * fs = tsk->fs;
-
-	if (fs) {
-		task_lock(tsk);
-		tsk->fs = NULL;
-		task_unlock(tsk);
-		put_fs_struct(fs);
-	}
-}
-
-EXPORT_SYMBOL_GPL(exit_fs);
-
 #ifdef CONFIG_MM_OWNER
 /*
  * Task p is exiting and it owned mm, lets find a new owner for it

kernel/fork.c

@@ -681,38 +681,13 @@ static int copy_mm(unsigned long clone_flags, struct task_struct * tsk)
 	return retval;
 }
 
-static struct fs_struct *__copy_fs_struct(struct fs_struct *old)
-{
-	struct fs_struct *fs = kmem_cache_alloc(fs_cachep, GFP_KERNEL);
-	/* We don't need to lock fs - think why ;-) */
-	if (fs) {
-		atomic_set(&fs->count, 1);
-		rwlock_init(&fs->lock);
-		fs->umask = old->umask;
-		read_lock(&old->lock);
-		fs->root = old->root;
-		path_get(&old->root);
-		fs->pwd = old->pwd;
-		path_get(&old->pwd);
-		read_unlock(&old->lock);
-	}
-	return fs;
-}
-
-struct fs_struct *copy_fs_struct(struct fs_struct *old)
-{
-	return __copy_fs_struct(old);
-}
-
-EXPORT_SYMBOL_GPL(copy_fs_struct);
-
 static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
 {
 	if (clone_flags & CLONE_FS) {
 		atomic_inc(&current->fs->count);
 		return 0;
 	}
-	tsk->fs = __copy_fs_struct(current->fs);
+	tsk->fs = copy_fs_struct(current->fs);
 	if (!tsk->fs)
 		return -ENOMEM;
 	return 0;
@@ -1545,7 +1520,7 @@ static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
 
 	if ((unshare_flags & CLONE_FS) &&
 	    (fs && atomic_read(&fs->count) > 1)) {
-		*new_fsp = __copy_fs_struct(current->fs);
+		*new_fsp = copy_fs_struct(current->fs);
 		if (!*new_fsp)
 			return -ENOMEM;
 	}