Feature Request: Add --offset option to mkfs.erofs

[Gao Xiang]

Hi,

On 2023/11/7 05:15, Павел Отчерцов wrote:
> Dear EROFS Developers,
> 
> I hope this message finds you well. I am reaching out to propose a feature addition to the `erofs-utils` that I believe could benefit many users, including myself.
> 
> As you know, `mksquashfs` offers an `-offset` option which allows users to specify an offset in the file where the filesystem will begin.
> This feature is particularly useful for embedding the SquashFS image into firmware images or other specific scenarios where filesystems must coexist with different data structures in a single image.
> 
> Currently, `mkfs.erofs` does not seem to support an equivalent option, which limits its utility in scenarios similar to those where `mksquashfs` is used.
> The addition of an `--offset` option to `mkfs.erofs` could provide users with the flexibility to specify the starting offset of the filesystem within an image file.
> 
> The syntax for this could be as straightforward as:
> 
> ```sh
> Copy code
> mkfs.erofs --offset=<offset-in-bytes> <destination-img> <source-directory>
> ```
> 
> This feature would align EROFS's functionality more closely with SquashFS, potentially broadening its use cases and adoption.
> 
> Currently, I can achieve a similar result by first creating an image file with the desired offset using `truncate`, and then concatenating the filesystem image to the offset image using `cat`, like so:
> 
> ```sh
> truncate -s <offset-in-bytes> image_with_offset.img
> cat erofs.img >> image_with_offset.img
> ```
> 
> However, this method is more cumbersome and less efficient than having an integrated option in `mkfs.erofs`.
> Implementing an `--offset` option would streamline the process and offer a more elegant and direct approach.
> 
> I understand that such features require time and resources to implement, and I appreciate the effort that goes into maintaining and improving open-source software.
> I believe this feature could enhance EROFS's utility for many users and look forward to any possibility of its inclusion in future releases.
> 
> Thank you for your consideration and for the work you do to develop and maintain EROFS. Please let me know if I can provide further information or assist in any way.

Thanks for the reference! Let's implement this feature.

Thanks,
Gao Xiang

> 
> Best regards,
> Pavel Otchertsov <pavel.otchertsov at gmail.com <mailto:pavel.otchertsov at gmail.com>>