> On 12. Jan 2023, at 00:21, Pedro Falcato <pedro.falcato@gmail.com> wrote:
>
> Several questions have popped up regarding the ext4 directory entry
> layout and contents off-list. Attempt to clarify these issues by adding
> some explanatory comments.
>
> Signed-off-by: Pedro Falcato <pedro.falcato@gmail.com>
> Cc: Marvin Häuser <mhaeuser@posteo.de>
> ---
> Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h | 18 +++++++++++++++++-
> Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h  |  3 +--
> 2 files changed, 18 insertions(+), 3 deletions(-)
>
> diff --git a/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h b/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h
> index 4fd91a423324..2dad967e575d 100644
> --- a/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h
> +++ b/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h
> @@ -397,12 +397,28 @@ typedef struct _Ext4Inode {
>   UINT32       i_projid;
> } EXT4_INODE;
>
> +#define EXT4_NAME_MAX  255
> +
> typedef struct {
> +  // ext4 directory entries are layed out in the

laid out

> following fashion:
> +  // offset 0x0: UINT32 inode number (if 0, unused entry, should skip.)
> +  // offset 0x4: UINT16 rec_len: Dir entry's length.
> +  //             Note: rec_len >= name_len + EXT4_MIN_DIR_ENTRY_LEN and rec_len % 4 == 0.
> +  // offset 0x6: UINT8 name_len: Dir entry's name's length
> +  // offset 0x7: UINT8 file_type Dir entry's file type indicator
> +  // offset 0x8: CHAR8 name[name_len]: Variable length character array; not null-terminated.

Why not document all that right above the member names? Would remove redundant info and be more Doxygen-friendly.

> +  //
> +  // Further note: ext4 directories are defined, as the documentation puts it, as:
> +  // "a directory is more or less a flat file that maps an arbitrary byte string
> +  // (usually ASCII) to an inode number on the filesystem". So, they are not
> +  // necessarily encoded with ASCII, UTF-8, or any of the sort. We must treat it
> +  // as a bag of bytes. When interacting with EFI interfaces themselves (which expect UCS-2)
> +  // we skip any directory entry that is not valid UTF-8.
>   UINT32    inode;
>   UINT16    rec_len;
>   UINT8     name_len;
>   UINT8     file_type;
> -  CHAR8     name[255];
> +  CHAR8     name[EXT4_NAME_MAX];
> } EXT4_DIR_ENTRY;
>
> #define EXT4_MIN_DIR_ENTRY_LEN  8
> diff --git a/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h b/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h
> index adf3c13f6ea9..81ba568c5947 100644
> --- a/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h
> +++ b/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h
> @@ -31,8 +31,7 @@
>
> #include "Ext4Disk.h"
>
> -#define SYMLOOP_MAX    8
> -#define EXT4_NAME_MAX  255
> +#define SYMLOOP_MAX  8
> //
> // We need to specify path length limit for security purposes, to prevent possible
> // overflows and dead-loop conditions. Originally this limit is absent in FS design,
> --
> 2.39.0
>