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fs: fat: handle deleted directory entries correctly

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Unlink test for FAT file system seems to fail at test_unlink2.
(When I added this test, I haven't seen any errors though.)
for example,
===8<===
fs_obj_unlink = ['fat', '/home/akashi/tmp/uboot_sandbox_test/128MB.fat32.img']

    def test_unlink2(self, u_boot_console, fs_obj_unlink):
        """
        Test Case 2 - delete many files
        """
        fs_type,fs_img = fs_obj_unlink
        with u_boot_console.log.section('Test Case 2 - unlink (many)'):
            output = u_boot_console.run_command('host bind 0 %s' % fs_img)

            for i in range(0, 20):
                output = u_boot_console.run_command_list([
                    '%srm host 0:0 dir2/0123456789abcdef%02x' % (fs_type, i),
                    '%sls host 0:0 dir2/0123456789abcdef%02x' % (fs_type, i)])
                assert('' == ''.join(output))

            output = u_boot_console.run_command(
                '%sls host 0:0 dir2' % fs_type)
>           assert('0 file(s), 2 dir(s)' in output)
E           AssertionError: assert '0 file(s), 2 dir(s)' in '            ./\r\r\n            ../\r\r\n        0   0123456789abcdef11\r\r\n\r\r\n1 file(s), 2 dir(s)'

test/py/tests/test_fs/test_unlink.py:52: AssertionError
===>8===

This can happen when fat_itr_next() wrongly detects an already-
deleted directory entry.

File deletion, which was added in the commit f8240ce95d ("fs: fat:
support unlink"), is implemented by marking its entry for a short name
with DELETED_FLAG, but related entry slots for a long file name are kept
unmodified. (So entries will never be actually deleted from media.)

To handle this case correctly, an additional check for a directory slot
will be needed in fat_itr_next().

In addition, I added extra comments about long file name and short file
name format in FAT file system. Although they are not directly related
to the issue, I hope it will be helpful for better understandings
in general.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
This commit is contained in:
AKASHI Takahiro 2019-11-26 17:29:31 +09:00 committed by Tom Rini
parent 2464b229b5
commit 39606d462c
1 changed files with 32 additions and 1 deletions
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33
fs/fat/fat.c
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@ -869,6 +869,14 @@ static dir_entry *extract_vfat_name(fat_itr *itr)
return NULL;
}
/*
* We are now at the short file name entry.
* If it is marked as deleted, just skip it.
*/
if (dent->name[0] == DELETED_FLAG ||
dent->name[0] == aRING)
return NULL;
itr->l_name[n] = '\0';
chksum = mkcksum(dent->name, dent->ext);
@ -898,6 +906,16 @@ static int fat_itr_next(fat_itr *itr)
itr->name = NULL;
/*
* One logical directory entry consist of following slots:
* name[0] Attributes
* dent[N - N]: LFN[N - 1] N|0x40 ATTR_VFAT
* ...
* dent[N - 2]: LFN[1] 2 ATTR_VFAT
* dent[N - 1]: LFN[0] 1 ATTR_VFAT
* dent[N]: SFN ATTR_ARCH
*/
while (1) {
dent = next_dent(itr);
if (!dent)
@ -910,7 +928,17 @@ static int fat_itr_next(fat_itr *itr)
if (dent->attr & ATTR_VOLUME) {
if ((dent->attr & ATTR_VFAT) == ATTR_VFAT &&
(dent->name[0] & LAST_LONG_ENTRY_MASK)) {
/* long file name */
dent = extract_vfat_name(itr);
/*
* If succeeded, dent has a valid short file
* name entry for the current entry.
* If failed, itr points to a current bogus
* entry. So after fetching a next one,
* it may have a short file name entry
* for this bogus entry so that we can still
* check for a short name.
*/
if (!dent)
continue;
itr->name = itr->l_name;
@ -919,8 +947,11 @@ static int fat_itr_next(fat_itr *itr)
/* Volume label or VFAT entry, skip */
continue;
}
}
} else if (!(dent->attr & ATTR_ARCH) &&
!(dent->attr & ATTR_DIR))
continue;
/* short file name */
break;
}