From a73a401d3140e5585b734b908068c2eaf597204a Mon Sep 17 00:00:00 2001
From: Neal Gompa <neal@gompa.dev>
Date: Wed, 22 Mar 2023 18:17:14 -0400
Subject: [PATCH 1/1] btrfs-progs: mkfs: Enforce 4k sectorsize by default

We have had working subpage support in Btrfs for many cycles now.
Generally, we do not want people creating filesystems by default
with non-4k sectorsizes since it creates portability problems.

Signed-off-by: Neal Gompa <neal@gompa.dev>

Reviewed-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
---
 Documentation/Subpage.rst    | 12 ++++++++----
 Documentation/mkfs.btrfs.rst | 13 +++++++++----
 mkfs/main.c                  |  2 +-
 3 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/Documentation/Subpage.rst b/Documentation/Subpage.rst
index bd1b41a8..62f2f924 100644
--- a/Documentation/Subpage.rst
+++ b/Documentation/Subpage.rst
@@ -9,14 +9,18 @@ to the exactly same size of the block and page. On x86_64 this is typically
 pages, like 64KiB on 64bit ARM or PowerPC. This means filesystems created
 with 64KiB sector size cannot be mounted on a system with 4KiB page size.
 
-While with subpage support, systems with 64KiB page size can create (still needs
-"-s 4k" option for :command:`mkfs.btrfs`) and mount filesystems with 4KiB sectorsize.
+Since v6.4, filesystems are created with a 4KiB sectorsize by default,
+though it remains possible to create filesystems with other page sizes
+(such as 64KiB with the "-s 64k" option for :command:`mkfs.btrfs`). This
+ensures that new filesystems are compatible across other architecture
+variants using larger page sizes.
 
 Requirements, limitations
 -------------------------
 
-The initial subpage support has been added in v5.15, although it's still
-considered as experimental, most features are already working without problems.
+The initial subpage support has been added in v5.15. Most features are
+already working without problems. Subpage support is used by default
+for systems with a non-4KiB page size since v6.4.
 
 End users can mount filesystems with 4KiB sectorsize and do their usual
 workload, while should not notice any obvious change, as long as the initial
diff --git a/Documentation/mkfs.btrfs.rst b/Documentation/mkfs.btrfs.rst
index d1626f73..47b8b05e 100644
--- a/Documentation/mkfs.btrfs.rst
+++ b/Documentation/mkfs.btrfs.rst
@@ -120,10 +120,15 @@ OPTIONS
 -s|--sectorsize <size>
         Specify the sectorsize, the minimum data block allocation unit.
 
-        The default value is the page size and is autodetected. If the sectorsize
-        differs from the page size, the created filesystem may not be mountable by the
-        running kernel. Therefore it is not recommended to use this option unless you
-        are going to mount it on a system with the appropriate page size.
+        By default, the value is 4KiB, but it can be manually set to match the
+        system page size. However, if the sector size is different from the page
+        size, the resulting filesystem may not be mountable by the current
+        kernel, apart from the default 4KiB. Hence, using this option is not
+        advised unless you intend to mount it on a system with the suitable
+        page size.
+
+        .. note::
+                Versions prior to 6.4 set the sectorsize matching to the page size.
 
 -L|--label <string>
         Specify a label for the filesystem. The *string* should be less than 256
diff --git a/mkfs/main.c b/mkfs/main.c
index 7acd39ec..5bac164d 100644
--- a/mkfs/main.c
+++ b/mkfs/main.c
@@ -1204,7 +1204,7 @@ int BOX_MAIN(mkfs)(int argc, char **argv)
 	}
 
 	if (!sectorsize)
-		sectorsize = (u32)sysconf(_SC_PAGESIZE);
+		sectorsize = (u32)SZ_4K;
 	if (btrfs_check_sectorsize(sectorsize))
 		goto error;
 
-- 
2.40.0