[PATCH v2 01/15] btrfs: add sysfs interface for supported sectorsize

[Qu Wenruo]

Add extra sysfs interface features/supported_ro_sectorsize and
features/supported_rw_sectorsize to indicate subpage support.

Currently for supported_rw_sectorsize all architectures only have their
PAGE_SIZE listed.

While for supported_ro_sectorsize, for systems with 64K page size, 4K
sectorsize is also supported.

This new sysfs interface would help mkfs.btrfs to do more accurate
warning.

Signed-off-by: Qu Wenruo <w...@suse.com>
---
 fs/btrfs/sysfs.c | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index 6eb1c50fa98c..3ef419899472 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -360,11 +360,45 @@ static ssize_t supported_rescue_options_show(struct 
kobject *kobj,
 BTRFS_ATTR(static_feature, supported_rescue_options,
           supported_rescue_options_show);
 
+static ssize_t supported_ro_sectorsize_show(struct kobject *kobj,
+                                           struct kobj_attribute *a,
+                                           char *buf)
+{
+       ssize_t ret = 0;
+       int i = 0;
+
+       /* For 64K page size, 4K sector size is supported */
+       if (PAGE_SIZE == SZ_64K) {
+               ret += scnprintf(buf + ret, PAGE_SIZE - ret, "%u", SZ_4K);
+               i++;
+       }
+       /* Other than above subpage, only support PAGE_SIZE as sectorsize yet */
+       ret += scnprintf(buf + ret, PAGE_SIZE - ret, "%s%lu\n",
+                        (i ? " " : ""), PAGE_SIZE);
+       return ret;
+}
+BTRFS_ATTR(static_feature, supported_ro_sectorsize,
+          supported_ro_sectorsize_show);
+
+static ssize_t supported_rw_sectorsize_show(struct kobject *kobj,
+                                           struct kobj_attribute *a,
+                                           char *buf)
+{
+       ssize_t ret = 0;
+
+       /* Only PAGE_SIZE as sectorsize is supported */
+       ret += scnprintf(buf + ret, PAGE_SIZE - ret, "%lu\n", PAGE_SIZE);
+       return ret;
+}
+BTRFS_ATTR(static_feature, supported_rw_sectorsize,
+          supported_rw_sectorsize_show);
 static struct attribute *btrfs_supported_static_feature_attrs[] = {
        BTRFS_ATTR_PTR(static_feature, rmdir_subvol),
        BTRFS_ATTR_PTR(static_feature, supported_checksums),
        BTRFS_ATTR_PTR(static_feature, send_stream_version),
        BTRFS_ATTR_PTR(static_feature, supported_rescue_options),
+       BTRFS_ATTR_PTR(static_feature, supported_ro_sectorsize),
+       BTRFS_ATTR_PTR(static_feature, supported_rw_sectorsize),
        NULL
 };
 
-- 
2.30.1