[U-Boot] [PATCH 1/2] fs/fat/fatwrite: Local variable as buffer to store dir_slot entries

Stephen Warren
2016-07-14T21:00:41Z

On 07/13/2016 03:01 AM, Tien Fong Chee wrote:
> fill_dir_slot use get_contents_vfatname_block as a temporary buffer for
> constructing a list of dir_slot entries. To save the memory and providing
> correct type of memory for above usage, a local buffer with accurate size
> declaration is introduced.
>
> The local array size 640 is used because for long file name entry,
> each entry use 32 bytes, one entry can store up to 13 characters.
> The maximum number of entry possible is 20. So, total size is
> 32*20=640bytes.

I'm fairly sure this series is correct[1], although the FAT write code
is a little hard to follow.

[1] except in the face of disk read errors or corrupted data while
parsing long filename entries, but the code already looks broken in the
case of disk errors, and the corrupted data case probably isn't much
worse now.

> diff --git a/include/fat.h b/include/fat.h

> +/* Maximum number of entry for long file name according to spec */
> +#define MAX_LFN_SLOT 20
> +
>
> /* Filesystem identifiers */
> #define FAT12_SIGN "FAT12 "

Why 2 blank lines there?

Also, I'd suggest simply deleting get_contents_vfatname_block and
renaming all references to it to use get_dentfromdir_block instead. That
way, anyone reading the code in the future won't assume the two "block"
variables refer to different memory, when in fact they share storage.
Related, there's little point keeping the now-redundant memcpy() call at
the end of get_long_file_name():

> memcpy(get_dentfromdir_block, get_contents_vfatname_block,
> mydata->clust_size * mydata->sect_size);