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Author: wedsonaf

samples/rust/rust_semaphore.rs

@@ -1,5 +1,16 @@
 // SPDX-License-Identifier: GPL-2.0
 
+//! A counting semaphore that can be used by userspace.
+//!
+//! The count is incremented by writes to the device. A write of `n` bytes results in an increment
+//! of `n`. It is decremented by reads; each read results in the count being decremented by 1. If
+//! the count is already zero, a read will block until another write increments it.
+//!
+//! This can be used in user space from the shell for example  as follows (assuming a node called
+//! `semaphore`): `cat semaphore` decrements the count by 1 (waiting for it to become non-zero
+//! before decrementing); `echo -n 123 > semaphore` increments the semaphore by 3, potentially
+//! unblocking up to 3 blocked readers.
+
 #![no_std]
 #![feature(allocator_api, global_asm)]
 

samples/rust/semaphore.c

@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 
+// This is a C implementation of `rust_semaphore.rs`. Refer to the description
+// in that file for details on the device.
 #include <linux/miscdevice.h>
 #include <linux/module.h>
 #include <linux/fs.h>