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    SubjectRe: [PATCH 27/39] union-mount: In-kernel copyup routines
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    On Mon, 03 May 2010 16:12:26 PDT, Valerie Aurora said:
    > 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 +++++++++++++++++++++++++++++++++++++++++++++++

    > +/**
    > + * 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;

    Should this be 'int error = 0;' ?

    > +
    > + 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;
    > +}

    because otherwise if do_splice_direct() returns a non-negative value,
    we can hit 'return error;' without ever having set error to anything?

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