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Subject[RFC][PATCH 10/14] In-kernel file copy between union mounted filesystems
From: Jan Blunck <j.blunck@tu-harburg.de>
Subject: 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_direct() for doing the in-kernel file copy.

Signed-off-by: Bharata B Rao <bharata@in.ibm.com>
Signed-off-by: Jan Blunck <j.blunck@tu-harburg.de>
---
fs/namei.c | 46 +++++
fs/union.c | 415 ++++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/namei.h | 2
include/linux/union.h | 14 +
4 files changed, 476 insertions(+), 1 deletion(-)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -830,8 +830,17 @@ done:
path->mnt = mnt;
path->dentry = dentry;

- if (nd->dentry->d_sb != dentry->d_sb)
+ /*
+ * This should be checked after the following of unions.
+ * Otherwise we might run into trouble creating directories
+ * on mountpoints. :(
+ * But maybe we shouldn't set the LAST_LOWLEVEL flag here
+ * at all ... */
+ if (nd->dentry->d_sb != dentry->d_sb) {
path->mnt = find_mnt(dentry);
+ UM_DEBUG_UID("Setting LAST_LOWLEVEL for %s\n", name->name);
+ nd->um_flags |= LAST_LOWLEVEL;
+ }

__follow_mount(path);
follow_union_mount(&path->mnt, &path->dentry);
@@ -950,6 +959,14 @@ static fastcall int __link_path_walk(con
if (err)
break;

+ if ((nd->flags & LOOKUP_TOPMOST) &&
+ (nd->um_flags & LAST_LOWLEVEL)) {
+ err = union_create_topdir(nd,&next.dentry,&next.mnt);
+ if (err)
+ goto out_dput;
+ nd->um_flags &= ~LAST_LOWLEVEL;
+ }
+
err = -ENOENT;
inode = next.dentry->d_inode;
if (!inode)
@@ -1005,6 +1022,15 @@ last_component:
err = do_lookup(nd, &this, &next);
if (err)
break;
+
+ if ((nd->flags & LOOKUP_TOPMOST) &&
+ (nd->um_flags & LAST_LOWLEVEL)) {
+ err = union_create_topdir(nd,&next.dentry,&next.mnt);
+ if (err)
+ goto out_dput;
+ nd->um_flags &= ~LAST_LOWLEVEL;
+ }
+
inode = next.dentry->d_inode;
if ((lookup_flags & LOOKUP_FOLLOW)
&& inode && inode->i_op && inode->i_op->follow_link) {
@@ -1177,6 +1203,7 @@ static int fastcall do_path_lookup(int d

nd->last_type = LAST_ROOT; /* if there are only slashes... */
nd->flags = flags;
+ nd->um_flags = 0;
nd->depth = 0;

if (*name=='/') {
@@ -1756,9 +1783,18 @@ int open_namei(int dfd, const char *path
nd, flag);
if (error)
return error;
+ /* test for WRONLY and RDWR - flag's special lower bits */
+ if (flag & 0x2) {
+ UM_DEBUG_UID("\"%s\" opened for writing\n", pathname);
+ error = union_copyup(nd, flag);
+ if (error)
+ return error;
+ }
goto ok;
}

+ UM_DEBUG_UID("open called with O_CREATE\n");
+
/*
* Create - we need to know the parent.
*/
@@ -1775,6 +1811,8 @@ int open_namei(int dfd, const char *path
if (nd->last_type != LAST_NORM || nd->last.name[nd->last.len])
goto exit;

+ UM_DEBUG_UID("do_last now\n");
+
dir = nd->dentry;
nd->flags &= ~LOOKUP_PARENT;
mutex_lock(&dir->d_inode->i_mutex);
@@ -1828,6 +1866,12 @@ do_last:
error = -EISDIR;
if (path.dentry->d_inode && S_ISDIR(path.dentry->d_inode->i_mode))
goto exit;
+
+ if (flag & 0x2) {
+ error = union_copyup(nd, flag);
+ if (error)
+ goto exit;
+ }
ok:
error = may_open(nd, acc_mode, flag);
if (error)
--- a/fs/union.c
+++ b/fs/union.c
@@ -15,6 +15,11 @@
#include <linux/module.h>
#include <linux/mount.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>

struct union_info * union_alloc(void)
{
@@ -305,6 +310,53 @@ void __dput_union(struct dentry *dentry)
return;
}

+/*
+ * 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;
+
+ UM_DEBUG_UID("relookup the topmost dir for %s\n",
+ nd->dentry->d_name.name);
+
+ 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;
+
+ /* If we are looking up the parent, copy the child details also */
+ if (flags & LOOKUP_PARENT) {
+ nd->last = this.last;
+ nd->last_type = this.last_type;
+ }
+
+ /*
+ * 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;
+}
+
void attach_mnt_union(struct vfsmount *mnt, struct nameidata *nd)
{
struct dentry *tmp;
@@ -975,6 +1027,37 @@ int follow_union_mount(struct vfsmount *
}

/*
+ * @stack is a already existing union stack, @new is a dentry or a union stack
+ * which is overlaid by @stack. So the topmost dentry is in @stack.
+ */
+static void append_to_stack(struct dentry *stack, struct dentry *new)
+{
+ struct dentry *topmost;
+ struct dentry *prev = stack;
+ struct dentry *next = new;
+
+ BUG_ON(!stack);
+ BUG_ON(!new);
+
+ while (prev->d_overlaid)
+ prev = prev->d_overlaid;
+
+ if (prev->d_topmost)
+ topmost = prev->d_topmost;
+ else
+ topmost = stack;
+
+ while (next) {
+ next->d_topmost = topmost;
+ prev->d_overlaid = next;
+ prev = next;
+ next = next->d_overlaid;
+ }
+
+ return;
+}
+
+/*
* Union mounts support for readdir.
*/

@@ -1372,3 +1455,335 @@ loff_t union_dir_llseek(struct file *fil
}
return -EINVAL;
}
+
+/*
+ * Union mount copyup support
+ */
+
+/*
+ * Just do what vfs_create() would do, but the union mount way
+ */
+static struct dentry * union_create(struct dentry *parent, struct dentry *old,
+ struct nameidata *nd)
+{
+ struct dentry *dentry;
+ int err, mode;
+
+ dentry = __lookup_hash_single(&old->d_name, parent, NULL);
+ if (IS_ERR(dentry))
+ goto exit;
+
+ err = -EEXIST;
+ if (dentry->d_inode) {
+ dput(dentry);
+ goto error;
+ }
+
+ err = -ENOENT;
+ if (IS_DEADDIR(parent->d_inode))
+ goto error;
+ err = -EACCES; /* shouldn't it be ENOSYS? */
+ if (!parent->d_inode->i_op || !parent->d_inode->i_op->create)
+ goto error;
+
+ mode = old->d_inode->i_mode & S_IALLUGO;
+ mode |= S_IFREG;
+
+ err = security_inode_create(parent->d_inode, dentry, mode);
+ if (err)
+ goto error;
+
+ DQUOT_INIT(parent->d_inode);
+ err = parent->d_inode->i_op->create(parent->d_inode, dentry, mode, nd);
+ if (err)
+ goto error;
+
+ dentry->d_inode->i_uid = old->d_inode->i_uid;
+ dentry->d_inode->i_gid = old->d_inode->i_gid;
+ mark_inode_dirty(dentry->d_inode);
+exit:
+ return dentry;
+error:
+ return ERR_PTR(err);
+}
+
+/*
+ * Just do what vfs_mkdir() would do, but the union mount way
+ */
+static struct dentry * union_mkdir(struct dentry *parent, struct dentry *dir)
+{
+ struct dentry *dentry;
+ int err, mode;
+
+ dentry = __lookup_hash_single(&dir->d_name, parent, NULL);
+ if (IS_ERR(dentry))
+ goto exit;
+
+ err = -EEXIST;
+ if (dentry->d_inode) {
+ dput(dentry);
+ goto error;
+ }
+
+ err = -ENOENT;
+ if (IS_DEADDIR(parent->d_inode))
+ goto error;
+ err = -EPERM;
+ if (!parent->d_inode->i_op || !parent->d_inode->i_op->mkdir)
+ goto error;
+
+ mode = dir->d_inode->i_mode & (S_IRWXUGO|S_ISVTX);
+
+ err = security_inode_mkdir(parent->d_inode, dentry, mode);
+ if (err)
+ goto error;
+
+ DQUOT_INIT(parent->d_inode);
+ err = parent->d_inode->i_op->mkdir(parent->d_inode, dentry, mode);
+ if (err)
+ goto error;
+
+ dentry->d_inode->i_uid = dir->d_inode->i_uid;
+ dentry->d_inode->i_gid = dir->d_inode->i_gid;
+ mark_inode_dirty(dentry->d_inode);
+exit:
+ return dentry;
+error:
+ return ERR_PTR(err);
+}
+
+static void __update_fs_pwd(struct dentry *old, struct dentry *new)
+{
+ struct dentry *old_pwd = NULL;
+ struct vfsmount *old_pwdmnt = NULL;
+ struct vfsmount *new_pwdmnt = find_mnt(new);
+
+ write_lock(&current->fs->lock);
+ if (current->fs->pwd == old) {
+ old_pwd = current->fs->pwd;
+ old_pwdmnt = current->fs->pwdmnt;
+ current->fs->pwdmnt = mntget(new_pwdmnt);
+ current->fs->pwd = __dget(new);
+ UM_DEBUG_UID("replacing fs->pwd\n");
+ UM_DEBUG_UID("oldpwd: name=\"%s\", inode=%p, devname=%s\n",
+ old_pwd->d_name.name, old_pwd->d_inode,
+ old_pwdmnt->mnt_devname);
+ UM_DEBUG_UID("newpwd: name=\"%s\", inode=%p, devname=%s\n",
+ new->d_name.name, new->d_inode,
+ new_pwdmnt->mnt_devname);
+ }
+ write_unlock(&current->fs->lock);
+
+ if (old_pwd) {
+ __dput(old_pwd);
+ mntput(old_pwdmnt);
+ }
+
+ mntput(new_pwdmnt);
+
+ return;
+}
+
+struct dentry * union_create_topmost(struct nameidata *nd, struct dentry *old)
+{
+ struct dentry *dentry;
+ struct dentry *parent = nd->dentry;
+
+ UM_DEBUG_UID("dentry=%s\n", old->d_name.name);
+
+ BUG_ON(parent->d_sb == old->d_sb);
+ if (!S_ISREG(old->d_inode->i_mode)) {
+ UM_DEBUG("This filetype isn't supported!\n");
+ dentry = ERR_PTR(-EINVAL);
+ goto exit;
+ }
+
+ /*
+ * Create the topmost regular file here.
+ */
+ mutex_lock(&parent->d_inode->i_mutex);
+ dentry = union_create(parent, old, nd);
+ mutex_unlock(&parent->d_inode->i_mutex);
+ if (IS_ERR(dentry)) {
+ UM_DEBUG("some error occurred\n");
+ goto exit;
+ }
+
+exit:
+ return dentry;
+}
+
+int union_create_topdir(struct nameidata *nd,
+ struct dentry **dentry, struct vfsmount **mnt)
+{
+ struct dentry *topdir;
+ struct dentry *parent = nd->dentry;
+
+ UM_DEBUG_UID("dentry=%s\n", (*dentry)->d_name.name);
+
+ if (parent->d_sb == (*dentry)->d_sb)
+ return 0;
+
+ if (!S_ISDIR((*dentry)->d_inode->i_mode)) {
+ UM_DEBUG("Unsupported filetype!\n");
+ BUG();
+ }
+
+ /*
+ * Create the topmost directory here.
+ */
+ spin_lock(&(*dentry)->d_lock);
+ if (!(*dentry)->d_union) {
+ UM_DEBUG_LOCK("Allocate lock for \"%s\"\n",
+ (*dentry)->d_name.name);
+ (*dentry)->d_union = union_alloc();
+ spin_unlock(&(*dentry)->d_lock);
+ } else {
+ spin_unlock(&(*dentry)->d_lock);
+ union_lock(*dentry);
+ }
+ mutex_lock(&parent->d_inode->i_mutex);
+ topdir = union_mkdir(parent, *dentry);
+ if (IS_ERR(topdir)) {
+ UM_DEBUG("some error occurred\n");
+ mutex_unlock(&parent->d_inode->i_mutex);
+ union_unlock(*dentry);
+ return PTR_ERR(topdir);
+ }
+
+ spin_lock(&topdir->d_lock);
+ if (topdir->d_union) {
+ UM_DEBUG("Aaargh! topdir \"%s\" already has a lock?!\n",
+ topdir->d_name.name);
+ dump_stack();
+ }
+ topdir->d_union = union_get((*dentry)->d_union);
+ spin_unlock(&topdir->d_lock);
+ append_to_stack(topdir, *dentry);
+ __update_fs_pwd(*dentry, topdir);
+ *dentry = topdir;
+ mutex_unlock(&parent->d_inode->i_mutex);
+ union_unlock(*dentry);
+
+ if (nd->mnt != *mnt) {
+ mntput(*mnt);
+ *mnt = mntget(nd->mnt);
+ }
+
+ return 0;
+}
+
+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 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 dentry *dir;
+ struct dentry *dentry;
+ int err;
+
+ if (!union_is_member(nd->dentry, nd->mnt))
+ return 0;
+ if (!S_ISREG(nd->dentry->d_inode->i_mode))
+ return 0;
+
+ err = union_relookup_topmost(nd, nd->flags|LOOKUP_PARENT);
+ if (err)
+ return err;
+
+ dir = nd->dentry;
+ nd->flags &= ~LOOKUP_PARENT;
+ union_lock(nd->dentry);
+ mutex_lock(&dir->d_inode->i_mutex);
+ dentry = __lookup_hash_kern_union(&nd->last, nd->dentry, nd);
+ err = PTR_ERR(dentry);
+ if (IS_ERR(dentry)) {
+ mutex_unlock(&dir->d_inode->i_mutex);
+ union_unlock(nd->dentry);
+ return err;
+ }
+
+ mutex_unlock(&dir->d_inode->i_mutex);
+ union_unlock(nd->dentry);
+
+ err = -ENOENT;
+ if (!dentry->d_inode)
+ goto exit_dput;
+
+ follow_mount(&nd->mnt, &dentry);
+
+ err = -ENOENT;
+ if (!dentry->d_inode)
+ goto exit_dput;
+
+ if (dentry->d_parent != dir) {
+ struct dentry *tmp;
+ struct vfsmount *old_mnt;
+
+ UM_DEBUG_UID("already exists -> copy file\n");
+ tmp = union_create_topmost(nd, dentry);
+ if (IS_ERR(tmp))
+ goto exit_dput;
+
+ old_mnt = find_mnt(dentry);
+ err = union_copy_file(dentry, old_mnt, tmp, nd->mnt);
+ if (err) {
+ int ret = vfs_unlink(tmp->d_inode, tmp);
+ BUG_ON(ret);
+ /* FIXME: not sure if there are return value
+ * we should not BUG() on */
+ }
+ dput(dentry);
+ dentry = tmp;
+ mntput(old_mnt);
+ }
+
+ dput(nd->dentry);
+ nd->dentry = dentry;
+ return 0;
+
+exit_dput:
+ dput(dentry);
+ return err;
+}
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -59,6 +59,8 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LA
#define LOOKUP_PARENT 16
#define LOOKUP_NOALT 32
#define LOOKUP_REVAL 64
+#define LOOKUP_TOPMOST 128
+#define LOOKUP_WHT 256
/*
* Intent data
*/
--- a/include/linux/union.h
+++ b/include/linux/union.h
@@ -35,11 +35,25 @@ extern int readdir_union(struct file *,

extern loff_t union_dir_llseek(struct file *, loff_t, int);

+/* copy-up support */
+extern struct dentry * union_create_topmost(struct nameidata *, struct dentry *);
+extern int union_create_topdir(struct nameidata *, struct dentry **, struct vfsmount **);
+extern int union_is_member(struct dentry *, struct vfsmount *);
+extern int union_copy_file(struct dentry *, struct vfsmount *, struct dentry *, struct vfsmount *);
+extern int union_copyup(struct nameidata *, int);
+extern int union_relookup_topmost(struct nameidata *, int);
+
#else /* CONFIG_UNION_MOUNT */

#define attach_mnt_union(mnt,nd) do { /* empty */ } while (0)
#define detach_mnt_union(mnt,nd) do { /* empty */ } while (0)
#define follow_union_mount(x,y) do { /* empty */ } while (0)
+#define union_create_topmost(x,y) ({ BUG(); ERR_PTR(-EINVAL); })
+#define union_create_topdir(x,y,z) ({ (0); })
+#define union_is_member(x,y) ({ (0); })
+#define union_copy_file(dentry1,mnt1,dentry2,mnt2) ({ (0); })
+#define union_copyup(x,y) ({ (0); })
+#define union_relookup_topmost(x,y) ({ (0); })

#endif /* CONFIG_UNION_MOUNT */

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