When a file on the read-only layer of a union mount is altered, it
must be copied up to the topmost read-write layer. This patch creates
union_copyup() and its supporting routines.
---
fs/union.c | 244 +++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/union.h | 7 +-
2 files changed, 250 insertions(+), 1 deletions(-)
diff --git a/fs/union.c b/fs/union.c
index 7e05698..d52c7c0 100644
--- a/fs/union.c
+++ b/fs/union.c
@@ -26,6 +26,7 @@
#include <linux/namei.h>
#include <linux/file.h>
#include <linux/security.h>
+#include <linux/splice.h>
/*
* This is borrowed from fs/inode.c. The hashtable for lookups. Somebody
@@ -630,3 +631,246 @@ out_fput:
mnt_drop_write(topmost_path->mnt);
return res;
}
+
+/**
+ * union_create_file
+ *
+ * @nd: namediata for source file
+ * @old: path of the source file
+ * @new: path of the new file, negative dentry
+ *
+ * Must already have mnt_want_write() on the mnt and the parent's
+ * i_mutex.
+ */
+
+static int union_create_file(struct nameidata *nd, struct path *old,
+ struct dentry *new)
+{
+ struct path *parent = &nd->path;
+ BUG_ON(!mutex_is_locked(&parent->dentry->d_inode->i_mutex));
+
+ return vfs_create(parent->dentry->d_inode, new,
+ old->dentry->d_inode->i_mode, nd);
+}
+
+/**
+ * union_create_symlink
+ *
+ * @nd: namediata for source symlink
+ * @old: path of the source symlink
+ * @new: path of the new symlink, negative dentry
+ *
+ * Must already have mnt_want_write() on the mnt and the parent's
+ * i_mutex.
+ */
+
+static int union_create_symlink(struct nameidata *nd, struct path *old,
+ struct dentry *new)
+{
+ void *cookie;
+ int error;
+
+ BUG_ON(!mutex_is_locked(&nd->path.dentry->d_inode->i_mutex));
+ /*
+ * We want the contents of this symlink, not to follow it, so
+ * this is modeled on generic_readlink() rather than
+ * do_follow_link().
+ */
+ nd->depth = 0;
+ cookie = old->dentry->d_inode->i_op->follow_link(old->dentry, nd);
+ if (IS_ERR(cookie))
+ return PTR_ERR(cookie);
+ /* Create a copy of the link on the top layer */
+ error = vfs_symlink(nd->path.dentry->d_inode, new,
+ nd_get_link(nd));
+ if (old->dentry->d_inode->i_op->put_link)
+ old->dentry->d_inode->i_op->put_link(old->dentry, nd, cookie);
+ return error;
+}
+
+/**
+ * union_copyup_data - Copy up len bytes of old's data to new
+ *
+ * @old: source file
+ * @new: target file
+ * @len: number of bytes to copy
+ */
+
+static int union_copyup_data(struct path *old, struct vfsmount *new_mnt,
+ struct dentry *new_dentry, size_t len)
+{
+ struct file *old_file;
+ struct file *new_file;
+ const struct cred *cred = current_cred();
+ loff_t offset = 0;
+ long bytes;
+ int error;
+
+ if (len == 0)
+ return 0;
+
+ /* Get reference to balance later fput() */
+ path_get(old);
+ old_file = dentry_open(old->dentry, old->mnt, O_RDONLY, cred);
+ 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, cred);
+ if (IS_ERR(new_file)) {
+ error = PTR_ERR(new_file);
+ goto out_fput;
+ }
+
+ bytes = do_splice_direct(old_file, &offset, new_file, len,
+ SPLICE_F_MOVE);
+ if (bytes < 0)
+ error = bytes;
+
+ fput(new_file);
+out_fput:
+ fput(old_file);
+ return error;
+}
+
+/**
+ * union_do_copyup_path_len - Copy up a file and len bytes of data
+ *
+ * @parent: parent directory's path
+ * @path: path of file to be copied up
+ * @len: number of bytes of file data to copy up
+ *
+ * Parent's i_mutex must be held by caller. Newly copied up path is
+ * returned in @path and original is path_put().
+ */
+
+static int __union_copyup_len(struct nameidata *nd, struct path *path,
+ size_t len)
+{
+ struct path *parent = &nd->path;
+ struct dentry *dentry;
+ int error;
+
+ BUG_ON(!mutex_is_locked(&parent->dentry->d_inode->i_mutex));
+
+ dentry = lookup_one_len(path->dentry->d_name.name, parent->dentry,
+ path->dentry->d_name.len);
+ if (IS_ERR(dentry))
+ return PTR_ERR(dentry);
+
+ if (dentry->d_inode) {
+ /*
+ * We raced with someone else and "lost." That's
+ * okay, they did all the work of copying up the file.
+ * Note that currently data copyup happens under the
+ * parent dir's i_mutex. If we move it outside that,
+ * we'll need some way of waiting for the data copyup
+ * to complete here.
+ */
+ error = 0;
+ goto out_newpath;
+ }
+ if (S_ISREG(path->dentry->d_inode->i_mode)) {
+ /* Create file */
+ error = union_create_file(nd, path, dentry);
+ if (error)
+ goto out_dput;
+ /* Copyup data */
+ error = union_copyup_data(path, parent->mnt, dentry, len);
+ } else {
+ BUG_ON(!S_ISLNK(path->dentry->d_inode->i_mode));
+ error = union_create_symlink(nd, path, dentry);
+ }
+ if (error) {
+ /* Most likely error: ENOSPC */
+ vfs_unlink(parent->dentry->d_inode, dentry);
+ goto out_dput;
+ }
+ /* XXX Copyup xattrs and any other dangly bits */
+out_newpath:
+ /* path_put() of original must happen before we copy in new */
+ path_put(path);
+ path->dentry = dentry;
+ path->mnt = mntget(parent->mnt);
+ return error;
+out_dput:
+ /* Don't path_put(path), let caller unwind */
+ dput(dentry);
+ return error;
+}
+
+/**
+ * union_copyup_path - Copy up a file given its path (and its parent's)
+ *
+ * @parent: parent directory's path
+ * @path: path of file to be copied up
+ * @newpath: return path of newly copied up file
+ * @copy_all: if set, copy all of the file's data and ignore @len
+ * @len: if @copy_all is not set, number of bytes of file data to copy up
+ */
+
+int do_union_copyup_len(struct nameidata *nd, struct path *path, int copy_all,
+ size_t len)
+{
+ struct path *parent = &nd->path;
+ int error;
+
+ if (!IS_UNIONED_DIR(parent))
+ return 0;
+ if (parent->mnt == path->mnt)
+ return 0;
+ if (!S_ISREG(path->dentry->d_inode->i_mode) &&
+ !S_ISLNK(path->dentry->d_inode->i_mode))
+ return 0;
+
+ BUG_ON(!S_ISDIR(parent->dentry->d_inode->i_mode));
+
+ mutex_lock(&parent->dentry->d_inode->i_mutex);
+ error = -ENOENT;
+ if (IS_DEADDIR(parent->dentry->d_inode))
+ goto out_unlock;
+
+ if (copy_all && S_ISREG(path->dentry->d_inode->i_mode)) {
+ error = -EFBIG;
+ len = i_size_read(path->dentry->d_inode);
+ if (((size_t)len != len) || ((ssize_t)len != len))
+ goto out_unlock;
+ }
+
+ error = __union_copyup_len(nd, path, len);
+
+out_unlock:
+ mutex_unlock(&parent->dentry->d_inode->i_mutex);
+ return error;
+}
+
+/*
+ * Helper function to copy up all of a file
+ */
+int union_copyup(struct nameidata *nd, struct path *path)
+{
+ return do_union_copyup_len(nd, path, 1, 0);
+}
+
+/*
+ * Unlocked helper function to copy up all of a file
+ */
+int __union_copyup(struct nameidata *nd, struct path *path)
+{
+ size_t len;
+ len = i_size_read(path->dentry->d_inode);
+ if (((size_t)len != len) || ((ssize_t)len != len))
+ return -EFBIG;
+
+ return __union_copyup_len(nd, path, len);
+}
+
+/*
+ * Helper function to copy up part of a file
+ */
+int union_copyup_len(struct nameidata *nd, struct path *path, size_t len)
+{
+ return do_union_copyup_len(nd, path, 0, len);
+}
+
diff --git a/include/linux/union.h b/include/linux/union.h
index fdd46f6..fbfea1d 100644
--- a/include/linux/union.h
+++ b/include/linux/union.h
@@ -52,7 +52,9 @@ extern struct dentry * union_create_topmost_dir(struct path *, struct qstr *,
extern int attach_mnt_union(struct vfsmount *, struct vfsmount *);
extern void detach_mnt_union(struct vfsmount *);
extern int union_copyup_dir(struct path *);
-
+extern int union_copyup(struct nameidata *, struct path *);
+extern int __union_copyup(struct nameidata *, struct path *);
+extern int union_copyup_len(struct nameidata *, struct path *, size_t len);
#else /* CONFIG_UNION_MOUNT */
#define IS_MNT_UNION(x) (0)
@@ -66,6 +68,9 @@ extern int union_copyup_dir(struct path *);
#define attach_mnt_union(x, y) do { } while (0)
#define detach_mnt_union(x) do { } while (0)
#define union_copyup_dir(x) ({ BUG(); (0); })
+#define union_copyup(x, y) ({ BUG(); (NULL); })
+#define __union_copyup(x, y) ({ BUG(); (NULL); })
+#define union_copyup_len(x, y, z) ({ BUG(); (NULL); })
#endif /* CONFIG_UNION_MOUNT */
#endif /* __KERNEL__ */
--
1.6.3.3
--
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