From 4d8199f0e3d30be69ebd10820d5402ec8d326e38 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    | 17 +++++++++--------

 Documentation/mkfs.btrfs.rst | 13 +++++++++----

 mkfs/main.c                  |  2 +-

 3 files changed, 19 insertions(+), 13 deletions(-)

diff --git a/Documentation/Subpage.rst b/Documentation/Subpage.rst

index c762b6a3..4bcfc6cf 100644

--- a/Documentation/Subpage.rst

+++ b/Documentation/Subpage.rst

@@ -9,18 +9,19 @@ 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

-and mount filesystems with 4KiB sectorsize.  This still needs to use option "-s

-4k" option for :command:`mkfs.btrfs`.

+Since v6.5, 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.

-On a 64KiB page system filesystem with 4KiB sectorsize can be mounted and used

-as usual as long as the initial mount succeeds. There are cases a mount will be

-rejected when verifying compatible features.

+The initial subpage support has been added in v5.15. Most features are

+already working without problems. On a 64KiB page system, a filesystem with

+4KiB sectorsize can be mounted and used as long as the initial mount succeeds.

+Subpage support is used by default for systems with a non-4KiB page size since v6.5.

 Please refer to status page of :ref:`status-subpage-block-size` for

 compatibility.

diff --git a/Documentation/mkfs.btrfs.rst b/Documentation/mkfs.btrfs.rst

index 1fca7448..d602fe9c 100644

--- a/Documentation/mkfs.btrfs.rst

+++ b/Documentation/mkfs.btrfs.rst

@@ -122,10 +122,15 @@ 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 1c5d668e..bd2e4350 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;

-- 

2.41.0