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Subject[RFC 21/26] union-mount: in-kernel file copy between union mounted filesystems
This patch introduces in-kernel file copy between union mounted
filesystems. When a file is opened for writing but resides on a lower (thus
read-only) layer of the union stack it is copied to the topmost union layer
first.

This patch uses the do_splice() for doing the in-kernel file copy.

Signed-off-by: Bharata B Rao <bharata@in.ibm.com>
Signed-off-by: Jan Blunck <jblunck@suse.de>
---
fs/namei.c | 73 ++++++++++-
fs/union.c | 312 ++++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/union.h | 9 +
3 files changed, 389 insertions(+), 5 deletions(-)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -994,7 +994,7 @@ static int __follow_mount(struct path *p
return res;
}

-static void follow_mount(struct vfsmount **mnt, struct dentry **dentry)
+void follow_mount(struct vfsmount **mnt, struct dentry **dentry)
{
while (d_mountpoint(*dentry)) {
struct vfsmount *mounted = lookup_mnt(*mnt, *dentry);
@@ -1213,6 +1213,21 @@ static fastcall int __link_path_walk(con
if (err)
break;

+ if ((nd->flags & LOOKUP_TOPMOST) &&
+ (nd->um_flags & LAST_LOWLEVEL)) {
+ struct dentry *dentry;
+
+ dentry = union_create_topmost(nd, &this, &next);
+ if (IS_ERR(dentry)) {
+ err = PTR_ERR(dentry);
+ goto out_dput;
+ }
+ dput_path(&next, nd);
+ next.mnt = nd->mnt;
+ next.dentry = dentry;
+ nd->um_flags &= ~LAST_LOWLEVEL;
+ }
+
err = -ENOENT;
inode = next.dentry->d_inode;
if (!inode || S_ISWHT(inode->i_mode))
@@ -1267,6 +1282,22 @@ last_component:
err = do_lookup(nd, &this, &next);
if (err)
break;
+
+ if ((nd->flags & LOOKUP_TOPMOST) &&
+ (nd->um_flags & LAST_LOWLEVEL)) {
+ struct dentry *dentry;
+
+ dentry = union_create_topmost(nd, &this, &next);
+ if (IS_ERR(dentry)) {
+ err = PTR_ERR(dentry);
+ goto out_dput;
+ }
+ dput_path(&next, nd);
+ next.mnt = nd->mnt;
+ next.dentry = dentry;
+ nd->um_flags &= ~LAST_LOWLEVEL;
+ }
+
inode = next.dentry->d_inode;
if ((lookup_flags & LOOKUP_FOLLOW)
&& inode && inode->i_op && inode->i_op->follow_link) {
@@ -1755,7 +1786,7 @@ out:
return err;
}

-static int hash_lookup_union(struct nameidata *nd, struct qstr *name,
+int hash_lookup_union(struct nameidata *nd, struct qstr *name,
struct path *path)
{
struct path safe = { .dentry = nd->dentry, .mnt = nd->mnt };
@@ -2169,6 +2200,11 @@ int open_namei(int dfd, const char *path
nd, flag);
if (error)
return error;
+ if (flag & FMODE_WRITE) {
+ error = union_copyup(nd, flag);
+ if (error)
+ return error;
+ }
goto ok;
}

@@ -2188,6 +2224,16 @@ int open_namei(int dfd, const char *path
if (nd->last_type != LAST_NORM || nd->last.name[nd->last.len])
goto exit;

+ /*
+ * If this dentry is on an union mount we need the topmost dentry here.
+ * This creates all topmost directories on the path to this dentry too.
+ */
+ if (is_unionized(nd->dentry, nd->mnt)) {
+ error = union_relookup_topmost(nd, nd->flags & ~LOOKUP_PARENT);
+ if (error)
+ goto exit;
+ }
+
dir = nd->dentry;
nd->flags &= ~LOOKUP_PARENT;
mutex_lock(&dir->d_inode->i_mutex);
@@ -2235,10 +2281,21 @@ do_last:
if (path.dentry->d_inode->i_op && path.dentry->d_inode->i_op->follow_link)
goto do_link;

- path_to_nameidata(&path, nd);
error = -EISDIR;
if (path.dentry->d_inode && S_ISDIR(path.dentry->d_inode->i_mode))
- goto exit;
+ goto exit_dput;
+
+ /*
+ * If this file is on a lower layer of the union stack, copy it to the
+ * topmost layer before opening it
+ */
+ if (path.dentry->d_inode && (path.dentry->d_parent != dir)) {
+ error = __union_copyup(&path, nd, &path);
+ if (error)
+ goto exit_dput;
+ }
+
+ path_to_nameidata(&path, nd);
ok:
error = may_open(nd, acc_mode, flag);
if (error)
@@ -3437,9 +3494,15 @@ static int do_rename(int olddfd, const c
error = -ENOTEMPTY;
if (new.dentry == trap)
goto exit5;
+ /* renaming on unions is done by the user-space */
+ error = -EXDEV;
+ if (is_unionized(oldnd.dentry, oldnd.mnt))
+ goto exit5;
+ if (is_unionized(newnd.dentry, newnd.mnt))
+ goto exit5;

error = vfs_rename(old_dir->d_inode, old.dentry,
- new_dir->d_inode, new.dentry);
+ new_dir->d_inode, new.dentry);
exit5:
dput_path(&new, &newnd);
exit4:
--- a/fs/union.c
+++ b/fs/union.c
@@ -20,6 +20,11 @@
#include <linux/union.h>
#include <linux/module.h>
#include <linux/file.h>
+#include <linux/mm.h>
+#include <linux/quotaops.h>
+#include <linux/dnotify.h>
+#include <linux/security.h>
+#include <linux/pipe_fs_i.h>

/*
* This is borrowed from fs/inode.c. The hashtable for lookups. Somebody
@@ -798,3 +803,310 @@ out:
union_cache_free(&cb.list);
return res;
}
+
+/*
+ * Union mount copyup support
+ */
+
+extern int hash_lookup_union(struct nameidata *, struct qstr *, struct path *);
+extern void follow_mount(struct vfsmount **, struct dentry **);
+
+/*
+ * union_relookup_topmost - lookup and create the topmost path to dentry
+ * @nd: pointer to nameidata
+ * @flags: lookup flags
+ */
+int union_relookup_topmost(struct nameidata *nd, int flags)
+{
+ int err;
+ char *kbuf, *name;
+ struct nameidata this;
+
+ kbuf = (char *)__get_free_page(GFP_KERNEL);
+ if (!kbuf)
+ return -ENOMEM;
+
+ name = d_path(nd->dentry, nd->mnt, kbuf, PAGE_SIZE);
+ err = PTR_ERR(name);
+ if (IS_ERR(name))
+ goto free_page;
+
+ err = path_lookup(name, flags|LOOKUP_CREATE|LOOKUP_TOPMOST, &this);
+ if (err)
+ goto free_page;
+
+ path_release(nd);
+ nd->dentry = this.dentry;
+ nd->mnt = this.mnt;
+
+ /*
+ * the nd->flags should be unchanged
+ */
+ BUG_ON(this.um_flags & LAST_LOWLEVEL);
+ nd->um_flags &= ~LAST_LOWLEVEL;
+ free_page:
+ free_page((unsigned long)kbuf);
+ return err;
+}
+
+static void __update_fs_pwd(struct path *path, struct dentry *dentry,
+ struct vfsmount *mnt)
+{
+ struct dentry *old_pwd = NULL;
+ struct vfsmount *old_pwdmnt = NULL;
+
+ write_lock(&current->fs->lock);
+ if (current->fs->pwd == path->dentry) {
+ old_pwd = current->fs->pwd;
+ old_pwdmnt = current->fs->pwdmnt;
+ current->fs->pwdmnt = mntget(mnt);
+ current->fs->pwd = dget(dentry);
+ }
+ write_unlock(&current->fs->lock);
+
+ if (old_pwd) {
+ dput(old_pwd);
+ mntput(old_pwdmnt);
+ }
+
+ return;
+}
+
+/*
+ * union_create_topmost - create the topmost path component
+ * @nd: pointer to nameidata of the base directory
+ * @name: pointer to file name
+ * @path: pointer to path of the overlaid file
+ *
+ * This is called by __link_path_walk() to create the directories on a path
+ * when it is called with LOOKUP_TOPMOST.
+ */
+struct dentry *union_create_topmost(struct nameidata *nd, struct qstr *name,
+ struct path *path)
+{
+ struct dentry *dentry, *parent = nd->dentry;
+ int res, mode = path->dentry->d_inode->i_mode;
+
+ if (parent->d_sb == path->dentry->d_sb)
+ return ERR_PTR(-EEXIST);
+
+ mutex_lock(&parent->d_inode->i_mutex);
+ dentry = lookup_one_len_nd(name->name, nd->dentry, name->len, nd);
+ if (IS_ERR(dentry))
+ goto out_unlock;
+
+ switch (mode & S_IFMT) {
+ case S_IFREG:
+ /*
+ * FIXME: Does this make any sense in this case?
+ * Special case - lookup gave negative, but... we had foo/bar/
+ * From the vfs_mknod() POV we just have a negative dentry -
+ * all is fine. Let's be bastards - you had / on the end,you've
+ * been asking for (non-existent) directory. -ENOENT for you.
+ */
+ if (name->name[name->len] && !dentry->d_inode) {
+ dput(dentry);
+ dentry = ERR_PTR(-ENOENT);
+ goto out_unlock;
+ }
+
+ res = vfs_create(parent->d_inode, dentry, mode, nd);
+ if (res) {
+ dput(dentry);
+ dentry = ERR_PTR(res);
+ goto out_unlock;
+ }
+ break;
+ case S_IFDIR:
+ res = vfs_mkdir(parent->d_inode, dentry, mode);
+ if (res) {
+ dput(dentry);
+ dentry = ERR_PTR(res);
+ goto out_unlock;
+ }
+
+ res = append_to_union(nd->mnt, dentry, path->mnt,
+ path->dentry);
+ if (res) {
+ dput(dentry);
+ dentry = ERR_PTR(res);
+ goto out_unlock;
+ }
+ break;
+ default:
+ dput(dentry);
+ dentry = ERR_PTR(-EINVAL);
+ goto out_unlock;
+ }
+
+ /* Really necessary ??? */
+/* __update_fs_pwd(path, dentry, nd->mnt); */
+
+ out_unlock:
+ mutex_unlock(&parent->d_inode->i_mutex);
+ return dentry;
+}
+
+static int union_copy_file(struct dentry *old_dentry, struct vfsmount *old_mnt,
+ struct dentry *new_dentry, struct vfsmount *new_mnt)
+{
+ int ret;
+ size_t size;
+ loff_t offset;
+ struct file *old_file, *new_file;
+
+ dget(old_dentry);
+ mntget(old_mnt);
+ old_file = dentry_open(old_dentry, old_mnt, O_RDONLY);
+ if (IS_ERR(old_file))
+ return PTR_ERR(old_file);
+
+ dget(new_dentry);
+ mntget(new_mnt);
+ new_file = dentry_open(new_dentry, new_mnt, O_WRONLY);
+ ret = PTR_ERR(new_file);
+ if (IS_ERR(new_file))
+ goto fput_old;
+
+ size = i_size_read(old_file->f_path.dentry->d_inode);
+ if (((size_t)size != size) || ((ssize_t)size != size)) {
+ ret = -EFBIG;
+ goto fput_new;
+ }
+
+ offset = 0;
+ ret = do_splice_direct(old_file, &offset, new_file, size,
+ SPLICE_F_MOVE);
+ if (ret >= 0)
+ ret = 0;
+ fput_new:
+ fput(new_file);
+ fput_old:
+ fput(old_file);
+ return ret;
+}
+
+/**
+ * __union_copyup - copy a file to the topmost directory
+ * @old: pointer to path of the old file name
+ * @new_nd: pointer to nameidata of the topmost directory
+ * @new: pointer to path of the new file name
+ *
+ * The topmost directory @new_nd must already be locked. Creates the topmost
+ * file if it doesn't exist yet.
+ */
+int __union_copyup(struct path *old, struct nameidata *new_nd, struct path *new)
+{
+ struct dentry *dentry;
+ int error;
+
+ /* Maybe this should be -EINVAL */
+ if (S_ISDIR(old->dentry->d_inode->i_mode))
+ return -EISDIR;
+
+ if (new_nd->dentry != new->dentry->d_parent) {
+ dentry = lookup_one_len_nd(new->dentry->d_name.name,
+ new_nd->dentry,
+ new->dentry->d_name.len, new_nd);
+ if (IS_ERR(dentry))
+ return PTR_ERR(dentry);
+ error = -EEXIST;
+ if (dentry->d_inode && !S_ISWHT(dentry->d_inode->i_mode))
+ goto out;
+ } else
+ dentry = new->dentry;
+
+ if (!dentry->d_inode) {
+ error = vfs_create(new_nd->dentry->d_inode, dentry,
+ old->dentry->d_inode->i_mode, new_nd);
+ if (error)
+ goto out;
+ }
+
+ error = union_copy_file(old->dentry, old->mnt, dentry, new_nd->mnt);
+ if (error) {
+ /* FIXME: are there return value we should not BUG() on ? */
+ BUG_ON(vfs_unlink(new_nd->dentry->d_inode, dentry));
+ goto out;
+ }
+
+ dput_path(new, new_nd);
+ new->dentry = dentry;
+ new->mnt = new_nd->mnt;
+out:
+ if (new->dentry != dentry)
+ dput(dentry);
+ return error;
+}
+
+/*
+ * union_copyup - copy a file to the topmost layer of the union stack
+ * @nd: nameidata pointer to the file
+ * @flags: flags given to open_namei
+ */
+int union_copyup(struct nameidata *nd, int flags)
+{
+ struct qstr this;
+ char *name;
+ struct dentry *dir;
+ struct path path;
+ int err;
+
+ if (!is_unionized(nd->dentry, nd->mnt))
+ return 0;
+ if (!S_ISREG(nd->dentry->d_inode->i_mode))
+ return 0;
+
+ /* safe the name for hash_lookup_union() */
+ this.len = nd->dentry->d_name.len;
+ this.hash = nd->dentry->d_name.hash;
+ name = kmalloc(this.len + 1, GFP_KERNEL);
+ if (!name)
+ return -ENOMEM;
+ this.name = name;
+ memcpy(name, nd->dentry->d_name.name, nd->dentry->d_name.len);
+ name[this.len] = 0;
+
+ err = union_relookup_topmost(nd, nd->flags|LOOKUP_PARENT);
+ if (err) {
+ kfree(name);
+ return err;
+ }
+ nd->flags &= ~LOOKUP_PARENT;
+
+ dir = nd->dentry;
+ mutex_lock(&dir->d_inode->i_mutex);
+ err = hash_lookup_union(nd, &this, &path);
+ mutex_unlock(&dir->d_inode->i_mutex);
+ kfree(name);
+ if (err)
+ return err;
+
+ err = -ENOENT;
+ if (!path.dentry->d_inode)
+ goto exit_dput;
+
+ /* Necessary?! I guess not ... */
+ follow_mount(&path.mnt, &path.dentry);
+
+ err = -ENOENT;
+ if (!path.dentry->d_inode)
+ goto exit_dput;
+
+ err = -EISDIR;
+ if (!S_ISREG(path.dentry->d_inode->i_mode))
+ goto exit_dput;
+
+ if (path.dentry->d_parent != nd->dentry) {
+ err = __union_copyup(&path, nd, &path);
+ if (err)
+ goto exit_dput;
+ }
+
+ path_to_nameidata(&path, nd);
+ return 0;
+
+exit_dput:
+ dput_path(&path, nd);
+ return err;
+}
--- a/include/linux/union.h
+++ b/include/linux/union.h
@@ -54,6 +54,11 @@ extern int attach_mnt_union(struct vfsmo
struct dentry *);
extern void detach_mnt_union(struct vfsmount *);
extern int readdir_union(struct file *, void *, filldir_t);
+extern int union_relookup_topmost(struct nameidata *, int);
+extern struct dentry *union_create_topmost(struct nameidata *, struct qstr *,
+ struct path *);
+extern int __union_copyup(struct path *, struct nameidata *, struct path *);
+extern int union_copyup(struct nameidata *, int);

#else /* CONFIG_UNION_MOUNT */

@@ -68,6 +73,10 @@ extern int readdir_union(struct file *,
#define __shrink_d_unions(x) do { } while (0)
#define attach_mnt_union(x, y, z) do { } while (0)
#define detach_mnt_union(x) do { } while (0)
+#define union_relookup_topmost(x, y) ({ BUG(); (0); })
+#define union_create_topmost(x, y, z) ({ BUG(); (NULL); })
+#define __union_copyup(x, y, z) ({ BUG(); (0); })
+#define union_copyup(x, y) ({ (0); })

#endif /* CONFIG_UNION_MOUNT */

--

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