Re: [edk2-devel] [PATCH 2/3] Ext4Pkg: Add documentation surrounding ext4 directory entries

["Pedro Falcato" <pedro.falcato@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 3575 bytes --]

Apologies for the duplicate send of these patches, small mistake using git
send-email *.patch ;)
Please only consider the patches that start with [PATCH N/3].

On Wed, Jan 11, 2023 at 11:59 PM Pedro Falcato via groups.io <pedro.falcato=
gmail.com@groups.io> 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 | 21 +++++++++++++++++++--
>  Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h  |  5 ++---
>  2 files changed, 21 insertions(+), 5 deletions(-)
>
> diff --git a/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h
> b/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h
> index 4fd91a423324..d0a455d0e572 100644
> --- a/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h
> +++ b/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h
> @@ -1,7 +1,7 @@
>  /** @file
>    Raw filesystem data structures
>
> -  Copyright (c) 2021 Pedro Falcato All rights reserved.
> +  Copyright (c) 2021 - 2023 Pedro Falcato All rights reserved.
>    SPDX-License-Identifier: BSD-2-Clause-Patent
>
>    Layout of an EXT2/3/4 filesystem:
> @@ -397,12 +397,29 @@ typedef struct _Ext4Inode {
>    UINT32       i_projid;
>  } EXT4_INODE;
>
> +#define EXT4_NAME_MAX  255
> +
>  typedef struct {
> +  // offset 0x0: inode number (if 0, unused entry, should skip.)
>    UINT32    inode;
> +  // offset 0x4: Directory entry's length.
> +  //             Note: rec_len >= name_len + EXT4_MIN_DIR_ENTRY_LEN and
> rec_len % 4 == 0.
>    UINT16    rec_len;
> +  // offset 0x6: Directory entry's name's length
>    UINT8     name_len;
> +  // offset 0x7: Directory entry's file type indicator
>    UINT8     file_type;
> -  CHAR8     name[255];
> +  // offset 0x8: name[name_len]: Variable length character array; not
> null-terminated.
> +  CHAR8     name[EXT4_NAME_MAX];
> +  // Further notes on names:
> +  // 1) We use EXT4_NAME_MAX here instead of flexible arrays for ease of
> use around the driver.
> +  //
> +  // 2) 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.
>  } 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..466e49523030 100644
> --- a/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h
> +++ b/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h
> @@ -1,7 +1,7 @@
>  /** @file
>    Common header for the driver
>
> -  Copyright (c) 2021 - 2022 Pedro Falcato All rights reserved.
> +  Copyright (c) 2021 - 2023 Pedro Falcato All rights reserved.
>    SPDX-License-Identifier: BSD-2-Clause-Patent
>  **/
>
> @@ -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
>
>
>
> 
>
>
>

-- 
Pedro

[-- Attachment #2: Type: text/html, Size: 4400 bytes --]