Merge patch series "fs: fat: calculate FAT type based on cluster count"

To quote the author:

This series fixes an issue where the FAT type (FAT12, FAT16) is not
correctly detected, e.g. when the BPB field BS_FilSysType contains the
valid value "FAT     ".

This issue occures, for example, if a partition is formatted by
swupdate using its diskformat handler. swupdate uses the FAT library
from http://elm-chan.org/fsw/ff/ internally.

See https://groups.google.com/g/swupdate/c/7Yc3NupjXx8 for a
discussion in the swupdate mailing list.

Please refer to the commit messages for more details.

1. Added bootsector checks

Most tests from https://www.win.tue.nl/~aeb/linux/fs/fat/fat-2.html
are added in the commit 'fs: fat: add bootsector validity check'.
Only the tests VIII, IX and X are not implemented.

I also checked the Linux kernel code (v6.6) and did not find any
checks on 'vistart->fs_type'. This is the reason why is skipped them
here.

See section '2. Size comparisons' for the impact on the binary size.

2. Size comparisons

I executed bloat-o-meter from the Linux kernel for an arm64
target (config xilinx_zynqmp_mini_emmc0_defconfig):

Comparison of the binary spl/u-boot-spl between master (rev
e17d174773e9ba9447596708e702b7382e47a6cf) and this patch
series (including the added validity checks of the boot sector):

add/remove: 0/0 grow/shrink: 1/1 up/down: 100/-12 (88)
Function                                     old     new   delta
read_bootsectandvi                           308     408    +100
fat_itr_root                                 444     432     -12
Total: Before=67977, After=68065, chg +0.13%

When compare the size of the binary spl/u-boot-spl between master this
series without the the validity checks of the boot sector:

add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-24 (-24)
Function                                     old     new   delta
read_bootsectandvi                           308     296     -12
fat_itr_root                                 444     432     -12
Total: Before=67977, After=67953, chg -0.04%

So the size of the spl on this arm64 target increases by 88 bytes for
this series. When i remove the validity check the size decreases by 24 bytes.

1 files changed, 50 insertions, 3 deletions

diff --git a/test/py/tests/test_fs/conftest.py b/test/py/tests/test_fs/conftest.py
index 0d87d180c7b..fdd138d6ee4 100644
--- a/test/py/tests/test_fs/conftest.py
+++ b/test/py/tests/test_fs/conftest.py
@@ -12,9 +12,10 @@ import u_boot_utils as util
 from tests import fs_helper
 
 supported_fs_basic = ['fat16', 'fat32', 'ext4']
-supported_fs_ext = ['fat16', 'fat32']
-supported_fs_mkdir = ['fat16', 'fat32']
-supported_fs_unlink = ['fat16', 'fat32']
+supported_fs_ext = ['fat12', 'fat16', 'fat32']
+supported_fs_fat = ['fat12', 'fat16']
+supported_fs_mkdir = ['fat12', 'fat16', 'fat32']
+supported_fs_unlink = ['fat12', 'fat16', 'fat32']
 supported_fs_symlink = ['ext4']
 
 #
@@ -49,6 +50,7 @@ def pytest_configure(config):
     """
     global supported_fs_basic
     global supported_fs_ext
+    global supported_fs_fat
     global supported_fs_mkdir
     global supported_fs_unlink
     global supported_fs_symlink
@@ -61,6 +63,7 @@ def pytest_configure(config):
         print('*** FS TYPE modified: %s' % supported_fs)
         supported_fs_basic =  intersect(supported_fs, supported_fs_basic)
         supported_fs_ext =  intersect(supported_fs, supported_fs_ext)
+        supported_fs_fat =  intersect(supported_fs, supported_fs_fat)
         supported_fs_mkdir =  intersect(supported_fs, supported_fs_mkdir)
         supported_fs_unlink =  intersect(supported_fs, supported_fs_unlink)
         supported_fs_symlink =  intersect(supported_fs, supported_fs_symlink)
@@ -83,6 +86,9 @@ def pytest_generate_tests(metafunc):
     if 'fs_obj_ext' in metafunc.fixturenames:
         metafunc.parametrize('fs_obj_ext', supported_fs_ext,
             indirect=True, scope='module')
+    if 'fs_obj_fat' in metafunc.fixturenames:
+        metafunc.parametrize('fs_obj_fat', supported_fs_fat,
+            indirect=True, scope='module')
     if 'fs_obj_mkdir' in metafunc.fixturenames:
         metafunc.parametrize('fs_obj_mkdir', supported_fs_mkdir,
             indirect=True, scope='module')
@@ -624,3 +630,44 @@ def fs_obj_symlink(request, u_boot_config):
     finally:
         call('rmdir %s' % mount_dir, shell=True)
         call('rm -f %s' % fs_img, shell=True)
+
+#
+# Fixture for fat test
+#
+@pytest.fixture()
+def fs_obj_fat(request, u_boot_config):
+    """Set up a file system to be used in fat test.
+
+    Args:
+        request: Pytest request object.
+        u_boot_config: U-Boot configuration.
+
+    Return:
+        A fixture for fat test, i.e. a duplet of file system type and
+        volume file name.
+    """
+
+    # the maximum size of a FAT12 filesystem resulting in 4084 clusters
+    MAX_FAT12_SIZE = 261695 * 1024
+
+    # the minimum size of a FAT16 filesystem that can be created with
+    # mkfs.vfat resulting in 4087 clusters
+    MIN_FAT16_SIZE = 8208 * 1024
+
+    fs_type = request.param
+    fs_img = ''
+
+    fs_ubtype = fstype_to_ubname(fs_type)
+    check_ubconfig(u_boot_config, fs_ubtype)
+
+    fs_size = MAX_FAT12_SIZE if fs_type == 'fat12' else MIN_FAT16_SIZE
+
+    try:
+        # the volume size depends on the filesystem
+        fs_img = fs_helper.mk_fs(u_boot_config, fs_type, fs_size, f'{fs_size}', 1024)
+    except:
+        pytest.skip('Setup failed for filesystem: ' + fs_type)
+        return
+    else:
+        yield [fs_ubtype, fs_img]
+    call('rm -f %s' % fs_img, shell=True)