[U-Boot] [PATCH] fs: add fs_readdir()

[Rob Clark]

On Thu, Aug 3, 2017 at 3:10 PM, Brüns, Stefan
<Stefan.Bruens at rwth-aachen.de> wrote:
> On Donnerstag, 3. August 2017 18:54:30 CEST Rob Clark wrote:
>> Needed to support efi file protocol.  The fallback.efi loader wants
>> to be able to read the contents of the /EFI directory to find an OS
>> to boot.
>>
>> Currently only implemented for FAT, but that is all that UEFI is
>> required to support.
>>
>> Signed-off-by: Rob Clark <robdclark at gmail.com>
>> ---
>>  fs/fat/fat.c  | 59
>> ++++++++++++++++++++++++++++++++++++++++++++++------------- fs/fs.c       |
>> 25 +++++++++++++++++++++++++
>>  include/fat.h |  4 +++-
>>  include/fs.h  | 21 +++++++++++++++++++++
>>  4 files changed, 95 insertions(+), 14 deletions(-)
>>
>
> NAK
>
> 1. The current code is already much to convoluted. Your changes add to this
> significantly

I agree with the first part of that statement, but not the second.
The code is pretty awful, but apparently works for people, and I don't
know (or have the time to learn) enough about FAT to do a massive
re-write.

I'll split this patch so we can add the interface without FAT
implementation, and I'll just carry around the second part downstream.

> 2. Your patch description neither references the exact part of the EFI
> specification you want to support (which took me some time, for reference it
> is "13.: Protocols - Media Access, 13.5: File Protocol"), nor are you
> specifying the required semantics (which is "open", "read", "close", where
> each read returns a single directory entry, similar to the POSIX opendir(),
> readdir() calls.

I can add a note in the commit message.. although I didn't really
think it would be too relevant to this patch.  (More relevant to the
patch which adds the efi_loader part, which depends on this patch.)

> 3. Usage of an index too lookup the next entry is also quite convoluted.
>
> 4. As far as I can see, your code will fail to find files in the root
> directory (look for LS_ROOT).

You could be right.. nothing ever traverses the root directory.

> I think it would be much better to first restructure the current code to use
> an readdir like interface internally, and then do everything EFI needs on top.

tbh, it would be nice even to implement fs_ls() generically on top of
readdir().. although I didn't do that since it would be slower
(without a re-write of FAT implementation, since we currently have to
re-traverse things for each readdir()).

BR,
-R

> This would get rid of the 4 almost identical copies to print the current
> directory entry (dols == LS_ROOT || dols == LS_YES), 2 copies of the remaining
> directory traversal and and also avoid the bug in (4.).
>
> Kind regards,
>
> Stefan