1 files changed, 130 insertions, 0 deletions

diff --git a/fs/file.c b/fs/file.c
index 754cd05b06af..7dbadaaf00f0 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -261,6 +261,136 @@ int expand_files(struct files_struct *files, int nr)
 	return expand_fdtable(files, nr);
 }
 
+static int count_open_files(struct fdtable *fdt)
+{
+	int size = fdt->max_fds;
+	int i;
+
+	/* Find the last open fd */
+	for (i = size/(8*sizeof(long)); i > 0; ) {
+		if (fdt->open_fds->fds_bits[--i])
+			break;
+	}
+	i = (i+1) * 8 * sizeof(long);
+	return i;
+}
+
+static struct files_struct *alloc_files(void)
+{
+	struct files_struct *newf;
+	struct fdtable *fdt;
+
+	newf = kmem_cache_alloc(files_cachep, GFP_KERNEL);
+	if (!newf)
+		goto out;
+
+	atomic_set(&newf->count, 1);
+
+	spin_lock_init(&newf->file_lock);
+	newf->next_fd = 0;
+	fdt = &newf->fdtab;
+	fdt->max_fds = NR_OPEN_DEFAULT;
+	fdt->close_on_exec = (fd_set *)&newf->close_on_exec_init;
+	fdt->open_fds = (fd_set *)&newf->open_fds_init;
+	fdt->fd = &newf->fd_array[0];
+	INIT_RCU_HEAD(&fdt->rcu);
+	fdt->next = NULL;
+	rcu_assign_pointer(newf->fdt, fdt);
+out:
+	return newf;
+}
+
+/*
+ * Allocate a new files structure and copy contents from the
+ * passed in files structure.
+ * errorp will be valid only when the returned files_struct is NULL.
+ */
+struct files_struct *dup_fd(struct files_struct *oldf, int *errorp)
+{
+	struct files_struct *newf;
+	struct file **old_fds, **new_fds;
+	int open_files, size, i;
+	struct fdtable *old_fdt, *new_fdt;
+
+	*errorp = -ENOMEM;
+	newf = alloc_files();
+	if (!newf)
+		goto out;
+
+	spin_lock(&oldf->file_lock);
+	old_fdt = files_fdtable(oldf);
+	new_fdt = files_fdtable(newf);
+	open_files = count_open_files(old_fdt);
+
+	/*
+	 * Check whether we need to allocate a larger fd array and fd set.
+	 * Note: we're not a clone task, so the open count won't change.
+	 */
+	if (open_files > new_fdt->max_fds) {
+		new_fdt->max_fds = 0;
+		spin_unlock(&oldf->file_lock);
+		spin_lock(&newf->file_lock);
+		*errorp = expand_files(newf, open_files-1);
+		spin_unlock(&newf->file_lock);
+		if (*errorp < 0)
+			goto out_release;
+		new_fdt = files_fdtable(newf);
+		/*
+		 * Reacquire the oldf lock and a pointer to its fd table
+		 * who knows it may have a new bigger fd table. We need
+		 * the latest pointer.
+		 */
+		spin_lock(&oldf->file_lock);
+		old_fdt = files_fdtable(oldf);
+	}
+
+	old_fds = old_fdt->fd;
+	new_fds = new_fdt->fd;
+
+	memcpy(new_fdt->open_fds->fds_bits,
+		old_fdt->open_fds->fds_bits, open_files/8);
+	memcpy(new_fdt->close_on_exec->fds_bits,
+		old_fdt->close_on_exec->fds_bits, open_files/8);
+
+	for (i = open_files; i != 0; i--) {
+		struct file *f = *old_fds++;
+		if (f) {
+			get_file(f);
+		} else {
+			/*
+			 * The fd may be claimed in the fd bitmap but not yet
+			 * instantiated in the files array if a sibling thread
+			 * is partway through open().  So make sure that this
+			 * fd is available to the new process.
+			 */
+			FD_CLR(open_files - i, new_fdt->open_fds);
+		}
+		rcu_assign_pointer(*new_fds++, f);
+	}
+	spin_unlock(&oldf->file_lock);
+
+	/* compute the remainder to be cleared */
+	size = (new_fdt->max_fds - open_files) * sizeof(struct file *);
+
+	/* This is long word aligned thus could use a optimized version */
+	memset(new_fds, 0, size);
+
+	if (new_fdt->max_fds > open_files) {
+		int left = (new_fdt->max_fds-open_files)/8;
+		int start = open_files / (8 * sizeof(unsigned long));
+
+		memset(&new_fdt->open_fds->fds_bits[start], 0, left);
+		memset(&new_fdt->close_on_exec->fds_bits[start], 0, left);
+	}
+
+	return newf;
+
+out_release:
+	kmem_cache_free(files_cachep, newf);
+out:
+	return NULL;
+}
+
 static void __devinit fdtable_defer_list_init(int cpu)
 {
 	struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu);