[U-Boot] [PATCH] fs: fat: handle deleted directory entries correctly

[AKASHI Takahiro]

On Tue, Nov 26, 2019 at 05:29:31PM +0900, AKASHI Takahiro wrote:
> Unlink test for FAT file system seems to fail at test_unlink2.
> (When I added this test, I haven't seen any errors though.)

FYI, once the following patches are merged, file system pytests
under /test/py/tests/test_fs will start to be invoked for sandbox build
on Travis CI.

[1] https://lists.denx.de/pipermail/u-boot/2019-November/391743.html
[2] https://lists.denx.de/pipermail/u-boot/2019-November/391742.html

Thanks,
-Takahiro Akashi


> 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 f8240ce95d64 ("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 at linaro.org>
> ---
>  fs/fat/fat.c | 33 ++++++++++++++++++++++++++++++++-
>  1 file changed, 32 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/fat/fat.c b/fs/fat/fat.c
> index 9e1b842dac6b..68ce65838678 100644
> --- a/fs/fat/fat.c
> +++ b/fs/fat/fat.c
> @@ -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;
>  	}
>  
> -- 
> 2.24.0
>