[PATCH v2 18/18] btrfs: allow RO mount of 4K sector size fs on 64K page system

[Qu Wenruo <wqu@suse.com>]

This adds the basic RO mount ability for 4K sector size on 64K page
system.

Currently we only plan to support 4K and 64K page system.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/disk-io.c | 24 +++++++++++++++++++++---
 fs/btrfs/super.c   |  7 +++++++
 2 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index adda76895058..8ab6308ff852 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2510,13 +2510,21 @@ static int validate_super(struct btrfs_fs_info *fs_info,
 		btrfs_err(fs_info, "invalid sectorsize %llu", sectorsize);
 		ret = -EINVAL;
 	}
-	/* Only PAGE SIZE is supported yet */
-	if (sectorsize != PAGE_SIZE) {
+
+	/*
+	 * For 4K page size, we only support 4K sector size.
+	 * For 64K page size, we support RW for 64K sector size, and RO for
+	 * 4K sector size.
+	 */
+	if ((SZ_4K == PAGE_SIZE && sectorsize != PAGE_SIZE) ||
+	    (SZ_64K == PAGE_SIZE && (sectorsize != SZ_4K &&
+				     sectorsize != SZ_64K))) {
 		btrfs_err(fs_info,
-			"sectorsize %llu not supported yet, only support %lu",
+			"sectorsize %llu not supported yet for page size %lu",
 			sectorsize, PAGE_SIZE);
 		ret = -EINVAL;
 	}
+
 	if (!is_power_of_2(nodesize) || nodesize < sectorsize ||
 	    nodesize > BTRFS_MAX_METADATA_BLOCKSIZE) {
 		btrfs_err(fs_info, "invalid nodesize %llu", nodesize);
@@ -3272,6 +3280,16 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device
 		goto fail_alloc;
 	}
 
+	/* For 4K sector size support, it's only read-only yet */
+	if (PAGE_SIZE == SZ_64K && sectorsize == SZ_4K) {
+		if (!sb_rdonly(sb) || btrfs_super_log_root(disk_super)) {
+			btrfs_err(fs_info,
+				"subpage sector size only support RO yet");
+			err = -EINVAL;
+			goto fail_alloc;
+		}
+	}
+
 	ret = btrfs_init_workqueues(fs_info, fs_devices);
 	if (ret) {
 		err = ret;
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 022f20810089..a8068c389d60 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1996,6 +1996,13 @@ static int btrfs_remount(struct super_block *sb, int *flags, char *data)
 			ret = -EINVAL;
 			goto restore;
 		}
+		if (fs_info->sectorsize < PAGE_SIZE) {
+			btrfs_warn(fs_info,
+	"read-write mount is not yet allowed for sector size %u page size %lu",
+				   fs_info->sectorsize, PAGE_SIZE);
+			ret = -EINVAL;
+			goto restore;
+		}
 
 		/*
 		 * NOTE: when remounting with a change that does writes, don't
-- 
2.29.2