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Subject[PATCH 64/73] union-mount: Implement union-aware truncate() [ver #2]
Date
Original-author: Valerie Aurora <vaurora@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com> (Further development)
---
fs/open.c | 44 ++++++++++++++++++++++++++++++++++++++------
1 files changed, 38 insertions(+), 6 deletions(-)
diff --git a/fs/open.c b/fs/open.c
index bce645b..f61183b 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -65,14 +65,17 @@ int do_truncate(struct dentry *dentry, loff_t length, unsigned int time_attrs,
static long do_sys_truncate(const char __user *pathname, loff_t length)
{
struct path path;
+ struct nameidata nd;
+ struct vfsmount *mnt;
struct inode *inode;
+ char *tmp;
int error;

error = -EINVAL;
if (length < 0) /* sorry, but loff_t says... */
goto out;

- error = user_path(pathname, &path);
+ error = user_path_nd(AT_FDCWD, pathname, 0, &nd, &path, &tmp);
if (error)
goto out;
inode = path.dentry->d_inode;
@@ -86,18 +89,45 @@ static long do_sys_truncate(const char __user *pathname, loff_t length)
if (!S_ISREG(inode->i_mode))
goto dput_and_out;

- error = mnt_want_write(path.mnt);
+ /* If we're looking at the lower layer of a union mount, then we need
+ * to create the file on the upperfs and truncate that.
+ */
+ if (IS_MNT_LOWER(path.mnt))
+ mnt = nd.path.mnt;
+ else
+ mnt = path.mnt;
+
+ error = mnt_want_write(mnt);
if (error)
goto dput_and_out;

- error = inode_permission(inode, MAY_WRITE);
- if (error)
- goto mnt_drop_write_and_out;
+ if (unlikely(IS_MNT_UNION(mnt))) {
+ /* We have to be able to write to the upperfs. */
+ error = -EROFS;
+ if (mnt->mnt_sb->s_flags & MS_RDONLY)
+ goto mnt_drop_write_and_out;
+
+ /* But the lowerfs inode must offer write permission - if the
+ * lowerfs was mounted writably. */
+ error = __inode_permission(inode, MAY_WRITE);
+ if (error)
+ goto mnt_drop_write_and_out;
+ } else {
+ error = inode_permission(inode, MAY_WRITE);
+ if (error)
+ goto mnt_drop_write_and_out;
+ }

error = -EPERM;
if (IS_APPEND(inode))
goto mnt_drop_write_and_out;

+ error = union_copyup_len(&nd, &path, length);
+ if (error)
+ goto mnt_drop_write_and_out;
+
+ /* path may have changed after copyup */
+ inode = path.dentry->d_inode;
error = get_write_access(inode);
if (error)
goto mnt_drop_write_and_out;
@@ -119,9 +149,11 @@ static long do_sys_truncate(const char __user *pathname, loff_t length)
put_write_and_out:
put_write_access(inode);
mnt_drop_write_and_out:
- mnt_drop_write(path.mnt);
+ mnt_drop_write(mnt);
dput_and_out:
path_put(&path);
+ path_put(&nd.path);
+ putname(tmp);
out:
return error;
}


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