support SetPosition value 0xFFFFFFFFFFFFFFFF meaning SEEK_END

[sergeystepanovx]

Hi!

I'd like to propose the following fix:

• As per SetPosition description in UEFI Spec: https://uefi.org/sites/default/files/resources/UEFI%20Spec%202.8B%20May%202020.pdf Seeking to position 0xFFFFFFFFFFFFFFFF causes the current position to be set to the end of the file.

I understand the motivation for forbidding seeks past the end of the file in read-only drivers, but this value has a special meaning and it is already possible to set the position to the end of file by explicitly specifying its size or reading the entire file.

[pbatard]

You are correct.

This is actually something I added in the other UEFI NTFS driver I have (which was written from the get go to be a lot more specs compliant than EfiFs), and that I was planning to retrofit into EfiFs, so thanks for sending a patch.