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.

4 files changed, 83 insertions, 8 deletions

diff --git a/test/image/spl_load_fs.c b/test/image/spl_load_fs.c
index 5f1de54..a89189e 100644
--- a/test/image/spl_load_fs.c
+++ b/test/image/spl_load_fs.c
@@ -220,7 +220,7 @@ static size_t create_fat(void *dst, size_t size, const char *filename,
 	bs->root_cluster = cpu_to_le32(root_sector);
 
 	vi->ext_boot_sign = 0x29;
-	memcpy(vi->fs_type, FAT32_SIGN, sizeof(vi->fs_type));
+	memcpy(vi->fs_type, "FAT32   ", sizeof(vi->fs_type));
 
 	memcpy(dst + 0x1fe, "\x55\xAA", 2);
 
diff --git a/test/py/tests/fs_helper.py b/test/py/tests/fs_helper.py
index 9882ddb..380f4c4 100644
--- a/test/py/tests/fs_helper.py
+++ b/test/py/tests/fs_helper.py
@@ -9,7 +9,7 @@ import re
 import os
 from subprocess import call, check_call, check_output, CalledProcessError
 
-def mk_fs(config, fs_type, size, prefix):
+def mk_fs(config, fs_type, size, prefix, size_gran = 0x100000):
     """Create a file system volume
 
     Args:
@@ -17,6 +17,7 @@ def mk_fs(config, fs_type, size, prefix):
         fs_type (str): File system type, e.g. 'ext4'
         size (int): Size of file system in bytes
         prefix (str): Prefix string of volume's file name
+        size_gran (int): Size granularity of file system image in bytes
 
     Raises:
         CalledProcessError: if any error occurs when creating the filesystem
@@ -24,7 +25,9 @@ def mk_fs(config, fs_type, size, prefix):
     fs_img = f'{prefix}.{fs_type}.img'
     fs_img = os.path.join(config.persistent_data_dir, fs_img)
 
-    if fs_type == 'fat16':
+    if fs_type == 'fat12':
+        mkfs_opt = '-F 12'
+    elif fs_type == 'fat16':
         mkfs_opt = '-F 16'
     elif fs_type == 'fat32':
         mkfs_opt = '-F 32'
@@ -36,7 +39,7 @@ def mk_fs(config, fs_type, size, prefix):
     else:
         fs_lnxtype = fs_type
 
-    count = (size + 0x100000 - 1) // 0x100000
+    count = (size + size_gran - 1) // size_gran
 
     # Some distributions do not add /sbin to the default PATH, where mkfs lives
     if '/sbin' not in os.environ["PATH"].split(os.pathsep):
@@ -44,7 +47,7 @@ def mk_fs(config, fs_type, size, prefix):
 
     try:
         check_call(f'rm -f {fs_img}', shell=True)
-        check_call(f'dd if=/dev/zero of={fs_img} bs=1M count={count}',
+        check_call(f'dd if=/dev/zero of={fs_img} bs={size_gran} count={count}',
                    shell=True)
         check_call(f'mkfs.{fs_lnxtype} {mkfs_opt} {fs_img}', shell=True)
         if fs_type == 'ext4':
diff --git a/test/py/tests/test_fs/conftest.py b/test/py/tests/test_fs/conftest.py
index 0d87d18..fdd138d 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)
diff --git a/test/py/tests/test_fs/test_fs_fat.py b/test/py/tests/test_fs/test_fs_fat.py
new file mode 100644
index 0000000..4009d0b
--- /dev/null
+++ b/test/py/tests/test_fs/test_fs_fat.py
@@ -0,0 +1,25 @@
+# SPDX-License-Identifier:      GPL-2.0+
+# Copyright (c) 2023 Weidmüller Interface GmbH & Co. KG
+# Author: Christian Taedcke <christian.taedcke@weidmueller.com>
+#
+# U-Boot File System: FAT Test
+
+"""
+This test verifies fat specific file system behaviour.
+"""
+
+import pytest
+import re
+
+@pytest.mark.boardspec('sandbox')
+@pytest.mark.slow
+class TestFsFat(object):
+    def test_fs_fat1(self, u_boot_console, fs_obj_fat):
+        """Test that `fstypes` prints a result which includes `sandbox`."""
+        fs_type,fs_img = fs_obj_fat
+        with u_boot_console.log.section('Test Case 1 - fatinfo'):
+            # Test Case 1 - ls
+            output = u_boot_console.run_command_list([
+                'host bind 0 %s' % fs_img,
+                'fatinfo host 0:0'])
+            assert(re.search('Filesystem: %s' % fs_type.upper(), ''.join(output)))