[U-Boot] [PATCH 2/2] fs/fat: Optimizes memory size with single global variable instead of 3

[Benoît Thébaudeau]

Hi,

On Tue, Aug 2, 2016 at 9:35 PM, Benoît Thébaudeau
<benoit.thebaudeau.dev at gmail.com> wrote:
> On Tue, Aug 2, 2016 at 8:53 PM, Stephen Warren <swarren at wwwdotorg.org> wrote:
>> On 07/28/2016 12:11 AM, Tien Fong Chee wrote:
>>>
>>> Single 64KB get_contents_vfatname_block global variable would be used for
>>> all FAT implementation instead of allocating additional two global
>>> variables
>>> which are get_denfromdir_block and do_fat_read_at_block. This
>>> implementation
>>> can help in saving up 128KB memory space.
>>
>>
>> The series,
>>
>> Tested-by: Stephen Warren <swarren at nvidia.com>
>> (via DFU's FAT reading/writing on various Tegra; likely primarily FAT rather
>> than VFAT though)
>>
>> Reviewed-by: Stephen Warren <swarren at nvidia.com>
>
> I suspect that reading a filename with VFAT entries crossing a cluster
> boundary in a FAT32 root directory will be broken by this series. I do
> not have time to test this and other corner cases right now though,
> but it will be possible in the next few weeks.

I have tested VFAT long filenames with the current implementation on
Sandbox. It's completely broken:
 - There is a length limit somewhere between 111 and 120 characters,
instead of 256 characters. Beyond this limit, the files are invisible
with ls.
 - Some filenames are truncated or mixed up between files. I have
tested 111-character random filenames for 1000 empty files in the root
directory. Most filenames had the expected length, but a few were
shorter or longer.
 - If there are too many files in the root directory, ls hangs.

I am pretty sure that this series introduces some regressions, but
they seem to be in corner cases that cannot even be used or tested
because of other bugs, so this series might not make this
implementation much more broken than it currently is. It's risky,
though.

I've quickly looked into TianoCore EDK II. It is so deeply tied to the
EFI driver model and APIs that it would be a pain to port to U-Boot.
Its FAT module is not designed to be portable beyond EFI. Its build
system would complicate things too.

Stephen, according to what you say in test/fs/fat-noncontig-test.sh,
your solution to accelerate FatFs seems to be working, even if the
author is not interested in it, so maybe it would still be worth
maintaining locally in order to have a reliable FAT support, also with
a small memory footprint. barebox uses FatFs.

Best regards,
Benoît