kernel_read_file(9)

okay so bestie, welcome to kernel_read_file(9) from the Kernel API Manual — the little kernel API that reads file contents into a kernel buffer, and we're gonna make it make sense 💅✨

🌸 NAME 🌸

kernel_read_file — read file contents into a kernel buffer

✨ SYNOPSIS ✨

ssize_t kernel_read_file (struct file *file , loff_t offset , void **buf
, size_t buf_size , size_t *file_size , enum kernel_read_file_id id );

🎀 ARGUMENTS 🎀

• file — the file to read from, literally.
• offset — where to start reading from (see below, bestie).
• buf — pointer to a "void *" buffer for reading into. If *buf is NULL, a buffer will be allocated, and buf_size will be ignored. no cap.
• buf_size — size of buf, if already allocated. If buf not allocated, this is the largest size to allocate.
• file_size — if non-NULL, the full size of file will be written here.
• id — the kernel_read_file_id identifying the type of file contents being read (for LSMs to examine, iykyk).

💅 DESCRIPTION 💅

okay so the offset situation is a whole vibe check: offset must be 0 unless both buf and file_size are non-NULL (i.e. the caller must be expecting to read partial file contents via an already-allocated buf, in at most buf_size chunks, and will be able to determine when the entire file was read by checking file_size). This isn't a recommended way to read a file, though, since it is possible that the contents might change between calls to kernel_read_file. 🫶

Returns number of bytes read (no single read will be bigger than SSIZE_MAX), or negative on error. periodt.

🦋 SEE ALSO 🦋

• Kernel file ./fs/kernel_read_file.c — that's the source file, go look 💖

this page is from source/version ./fs, dated October 2026, and it's the kernel_read_file(9) manual — mwah 💋🎀