[PATCH v4 3/4] btrfs: add force_chunk_alloc sysfs entry to force allocation

[Stefan Roesch <shr@fb.com>]

This adds the force_chunk_alloc sysfs entry to be able to force a
storage allocation. This is a debugging and test feature and is
enabled with the CONFIG_BTRFS_DEBUG configuration option.

It is stored at
/sys/fs/btrfs/<uuid>/allocation/<block_type>/force_chunk_alloc.
---
 fs/btrfs/sysfs.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)

diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index 3b0bcbc2ed2e..983c53b76aa6 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -771,6 +771,64 @@ static ssize_t btrfs_chunk_size_store(struct kobject *kobj,
 	return val;
 }
 
+#ifdef CONFIG_BTRFS_DEBUG
+/*
+ * Return if space info force allocation chunk flag is set.
+ */
+static ssize_t btrfs_force_chunk_alloc_show(struct kobject *kobj,
+					    struct kobj_attribute *a,
+					    char *buf)
+{
+	return snprintf(buf, PAGE_SIZE, "0\n");
+}
+
+/*
+ * Request chunk allocation with current chunk size.
+ */
+static ssize_t btrfs_force_chunk_alloc_store(struct kobject *kobj,
+					     struct kobj_attribute *a,
+					     const char *buf, size_t len)
+{
+	struct btrfs_space_info *space_info = to_space_info(kobj);
+	struct btrfs_fs_info *fs_info = to_fs_info(get_btrfs_kobj(kobj));
+	struct btrfs_trans_handle *trans;
+	unsigned long val;
+	int ret;
+
+	if (!fs_info) {
+		pr_err("couldn't get fs_info\n");
+		return -EPERM;
+	}
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	if (sb_rdonly(fs_info->sb))
+		return -EROFS;
+
+	ret = kstrtoul(buf, 10, &val);
+	if (ret)
+		return ret;
+
+	if (val == 0)
+		return -EINVAL;
+
+	/*
+	 * Allocate new chunk.
+	 */
+	trans = btrfs_start_transaction(fs_info->extent_root, 0);
+	if (!trans)
+		return PTR_ERR(trans);
+	ret = btrfs_force_chunk_alloc(trans, space_info->flags);
+	btrfs_end_transaction(trans);
+
+	if (ret == 1)
+		return len;
+
+	return -ENOSPC;
+}
+#endif
+
 SPACE_INFO_ATTR(flags);
 SPACE_INFO_ATTR(total_bytes);
 SPACE_INFO_ATTR(bytes_used);
@@ -783,6 +841,10 @@ SPACE_INFO_ATTR(disk_used);
 SPACE_INFO_ATTR(disk_total);
 BTRFS_ATTR_RW(space_info, chunk_size, btrfs_chunk_size_show,
 	      btrfs_chunk_size_store);
+#ifdef CONFIG_BTRFS_DEBUG
+BTRFS_ATTR_RW(space_info, force_chunk_alloc, btrfs_force_chunk_alloc_show,
+	      btrfs_force_chunk_alloc_store);
+#endif
 
 /*
  * Allocation information about block group types.
@@ -801,6 +863,9 @@ static struct attribute *space_info_attrs[] = {
 	BTRFS_ATTR_PTR(space_info, disk_used),
 	BTRFS_ATTR_PTR(space_info, disk_total),
 	BTRFS_ATTR_PTR(space_info, chunk_size),
+#ifdef CONFIG_BTRFS_DEBUG
+	BTRFS_ATTR_PTR(space_info, force_chunk_alloc),
+#endif
 	NULL,
 };
 ATTRIBUTE_GROUPS(space_info);
-- 
2.30.2