[PATCH v6 2/4] btrfs: expose chunk size in sysfs.

[Stefan Roesch <shr@fb.com>]

This adds a new sysfs entry in /sys/fs/btrfs/<uuid>/allocation/<block
type>/chunk_size. This allows to query the chunk size and also set the
chunk size.

Signed-off-by: Stefan Roesch <shr@fb.com>
---
 fs/btrfs/sysfs.c | 94 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 94 insertions(+)

diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index f9eff3b0f77c..39890ea21997 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -21,6 +21,7 @@
 #include "space-info.h"
 #include "block-group.h"
 #include "qgroup.h"
+#include "misc.h"
 
 /*
  * Structure name                       Path
@@ -92,6 +93,7 @@ static struct btrfs_feature_attr btrfs_attr_features_##_name = {	     \
 
 static inline struct btrfs_fs_info *to_fs_info(struct kobject *kobj);
 static inline struct btrfs_fs_devices *to_fs_devs(struct kobject *kobj);
+static inline struct kobject *get_btrfs_kobj(struct kobject *kobj);
 
 static struct btrfs_feature_attr *to_btrfs_feature_attr(struct kobj_attribute *a)
 {
@@ -708,6 +710,81 @@ static ssize_t btrfs_space_info_show_##field(struct kobject *kobj,	\
 }									\
 BTRFS_ATTR(space_info, field, btrfs_space_info_show_##field)
 
+/*
+ * Return space info chunk size.
+ */
+static ssize_t btrfs_chunk_size_show(struct kobject *kobj,
+				     struct kobj_attribute *a, char *buf)
+{
+	struct btrfs_space_info *sinfo = to_space_info(kobj);
+
+	return sysfs_emit(buf, "%llu\n", atomic64_read(&sinfo->chunk_size));
+}
+
+/*
+ * Store new user supplied chunk size in space info.
+ *
+ * Note: If the new chunk size value is larger than 10% of free space it is
+ *       reduced to match that limit.
+ */
+static ssize_t btrfs_chunk_size_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));
+	u64 val;
+	int ret;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	if (!fs_info) {
+		pr_err("couldn't get fs_info\n");
+		return -EPERM;
+	}
+
+	if (sb_rdonly(fs_info->sb))
+		return -EROFS;
+
+	if (!fs_info->fs_devices)
+		return -EINVAL;
+
+	if (btrfs_is_zoned(fs_info))
+		return -EINVAL;
+
+	if (!space_info) {
+		btrfs_err(fs_info, "couldn't get space_info\n");
+		return -EPERM;
+	}
+
+	/* System block type must not be changed. */
+	if (space_info->flags & BTRFS_BLOCK_GROUP_SYSTEM)
+		return -EINVAL;
+
+	ret = kstrtoull(buf, 10, &val);
+	if (ret)
+		return ret;
+
+	val = min(val, BTRFS_MAX_DATA_CHUNK_SIZE);
+
+	/*
+	 * Limit stripe size to 10% of available space.
+	 */
+	val = min(div_factor(fs_info->fs_devices->total_rw_bytes, 1), val);
+
+	/* Must be multiple of 256M. */
+	val &= ~(SZ_256M - 1);
+
+	/* Must be at least 256M. */
+	if (val < SZ_256M)
+		return -EINVAL;
+
+	btrfs_update_space_info_chunk_size(space_info, val);
+
+	return val;
+}
+
 SPACE_INFO_ATTR(flags);
 SPACE_INFO_ATTR(total_bytes);
 SPACE_INFO_ATTR(bytes_used);
@@ -718,6 +795,8 @@ SPACE_INFO_ATTR(bytes_readonly);
 SPACE_INFO_ATTR(bytes_zone_unusable);
 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);
 
 /*
  * Allocation information about block group types.
@@ -735,6 +814,7 @@ static struct attribute *space_info_attrs[] = {
 	BTRFS_ATTR_PTR(space_info, bytes_zone_unusable),
 	BTRFS_ATTR_PTR(space_info, disk_used),
 	BTRFS_ATTR_PTR(space_info, disk_total),
+	BTRFS_ATTR_PTR(space_info, chunk_size),
 	NULL,
 };
 ATTRIBUTE_GROUPS(space_info);
@@ -1099,6 +1179,20 @@ static inline struct btrfs_fs_info *to_fs_info(struct kobject *kobj)
 	return to_fs_devs(kobj)->fs_info;
 }
 
+/*
+ * Get btrfs sysfs kobject.
+ */
+static inline struct kobject *get_btrfs_kobj(struct kobject *kobj)
+{
+	while (kobj) {
+		if (kobj->ktype == &btrfs_ktype)
+			return kobj;
+		kobj = kobj->parent;
+	}
+
+	return NULL;
+}
+
 #define NUM_FEATURE_BITS 64
 #define BTRFS_FEATURE_NAME_MAX 13
 static char btrfs_unknown_feature_names[FEAT_MAX][NUM_FEATURE_BITS][BTRFS_FEATURE_NAME_MAX];
-- 
2.30.2