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);