CODEWITHSUNDEEP
clinuxkernelkernel-module
alexandernst
alexandernst

Reputation: 15109

Get file name/path from a file descriptor from a Linux kernel module?

In a linux kernel module is there a way to get a file name/path from an unsigned int fd?

I'm aware of this answer: How can I get a filename from a file descriptor inside a kernel module? but if I understand the code right, I need a struct files_struct too.

EDIT:

Please stop voting as duplicated as it isn't. I'm asking for a way to get file's name/path in plain C from a kernel module, not using system tools. Said in another way: running readlink on /procself/fd/ is not a good answer.

EDIT 2:

Kernel's syscall read ssize_t read(int fd, void *buf, size_t count); takes 3 arguments, one of them being a fd. It's obvious that somehow read is able to read from a single file (instead of all files inside an inode). The question is how.

Upvotes: 5

Views: 10482

Answers (1)

caf
caf

Reputation: 239041

The code in the answer to the question that you reference is what you need to do. And yes, a struct files_struct from a task is needed, because a file descriptor is only meaningful in the context of a files_struct (usually, there is one of these per process). File descriptors aren't globally unique, just an index within an individual open file table.

If your code is running in process-context (eg. invoked through a syscall) then you can use current->files for the current task's files_struct. This is what read() does.

Upvotes: 3

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