From 59363848a29fb18762a91023c1318922764bc843 Mon Sep 17 00:00:00 2001
From: Avril <flanchan@cumallover.me>
Date: Sat, 30 Apr 2022 22:46:01 +0100
Subject: [PATCH] Started: `memfile::hp`: `MFD_HUGETLB` can be used when a size
 is known to exceed into the boundary of a hugepage. Currently in the process
 of writing function to collect all possible hugepage sizes and generate the
 correct flag masks for `memfd_create(, MFD_HUGETLB | ...)` for each one; and
 the smallest one that contains the known size can be used for the
 `memfd_create()` call (if the size fits any at all.)
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TODO: This will be a seperate comptime feature: `hugetlb`: Extend `memfile` with the ability to allocate apporpirately sized huge-pages when input size is known to extend into them.

Fortune for collect's current commit: Blessing − 吉
---
 Cargo.lock        |  2 +-
 src/memfile.rs    |  3 +++
 src/memfile/hp.rs | 35 +++++++++++++++++++++++++++++++++++
 3 files changed, 39 insertions(+), 1 deletion(-)
 create mode 100644 src/memfile/hp.rs

diff --git a/Cargo.lock b/Cargo.lock
index 675a63a..b3b56d9 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -84,7 +84,7 @@ checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
 
 [[package]]
 name = "collect"
-version = "1.0.1"
+version = "1.0.2"
 dependencies = [
  "bitflags",
  "bytes",
diff --git a/src/memfile.rs b/src/memfile.rs
index a0e7431..50b6b5f 100644
--- a/src/memfile.rs
+++ b/src/memfile.rs
@@ -16,6 +16,9 @@ use std::{
 pub mod fd;
 pub mod error;
 mod map;
+//TODO: #[cfg(feature="hugetlb")] 
+mod hp;
+
 
 /// Flags passed to `memfd_create()` when used in this module
 const MEMFD_CREATE_FLAGS: libc::c_uint = libc::MFD_CLOEXEC;
diff --git a/src/memfile/hp.rs b/src/memfile/hp.rs
new file mode 100644
index 0000000..61e2235
--- /dev/null
+++ b/src/memfile/hp.rs
@@ -0,0 +1,35 @@
+//! # Huge pages
+//! Calculates available huge page sizes, and creates `memfd_create()` flag masks for a `MFD_HUGETLB` fd.
+use super::*;
+use std::{
+    path::Path,
+};
+use libc::{
+    MFD_HUGETLB,
+    MAP_HUGE_SHIFT,
+};
+
+/// The location in the kernel's API which shows all valid huge-page sizes.
+///
+/// This is a directory, and its subdirectories' *names* will contain the size in this format: `hugepages-(\d+)kB` (where the first capture-group is the size in kB.)
+/// The contents of those subdirectories themselves are irrelevent for our purpose.
+pub const HUGEPAGE_SIZES_LOCATION: &'static str = "/sys/kernel/mm/hugepages";
+
+/// Take a directory path and try to parse the hugepage size from it.
+///
+/// All subdirectories from `HUGEPAGE_SIZES_LOCATION` should be passed to this, and the correct system-valid hugepage size will be returned for that specific hugepage.
+fn find_size_bytes(path: impl AsRef<Path>) -> Option<usize>
+{
+    let path= path.as_ref();
+    if !path.is_dir() {
+	return None;
+    } 
+
+    let dir_name = path.file_name()?;
+    // location of the `-` in the dir name
+    let split_loc = memchr::memchr(b'-', dir_name.as_bytes())?;
+
+    //TODO: find the `k` (XXX: Is it always in kB? Or do we have to find the last non-digit byte instead?) For now, we can just memchr('k') I think -- look into kernel spec for this later.
+    
+    None
+}