From 3315f8fecfbba8bf3f15be3874ffdaee486d2601 Mon Sep 17 00:00:00 2001
From: Christopher Friedt <chrisfriedt@gmail.com>
Date: Wed, 6 May 2020 18:43:58 -0400
Subject: [PATCH] kernel: pipe: read_avail / write_avail syscalls

These helper functions may clarify how much data is available to read
from or write to the circular buffer of a k_pipe.

Fixes #25036

Signed-off-by: Christopher Friedt <chrisfriedt@gmail.com>
---
 include/kernel.h | 20 +++++++++++++
 kernel/pipes.c   | 74 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 94 insertions(+)

diff --git a/include/kernel.h b/include/kernel.h
index 9137666ff4b..e2de042322f 100644
--- a/include/kernel.h
+++ b/include/kernel.h
@@ -4430,6 +4430,26 @@ __syscall int k_pipe_get(struct k_pipe *pipe, void *data,
 extern void k_pipe_block_put(struct k_pipe *pipe, struct k_mem_block *block,
 			     size_t size, struct k_sem *sem);
 
+/**
+ * @brief Query the number of bytes that may be read from @a pipe.
+ *
+ * @param pipe Address of the pipe.
+ *
+ * @retval a number n such that 0 <= n <= @ref k_pipe.size; the
+ *         result is zero for unbuffered pipes.
+ */
+__syscall size_t k_pipe_read_avail(struct k_pipe *pipe);
+
+/**
+ * @brief Query the number of bytes that may be written to @a pipe
+ *
+ * @param pipe Address of the pipe.
+ *
+ * @retval a number n such that 0 <= n <= @ref k_pipe.size; the
+ *         result is zero for unbuffered pipes.
+ */
+__syscall size_t k_pipe_write_avail(struct k_pipe *pipe);
+
 /** @} */
 
 /**
diff --git a/kernel/pipes.c b/kernel/pipes.c
index 8b83c41ca32..d28d7a33cf6 100644
--- a/kernel/pipes.c
+++ b/kernel/pipes.c
@@ -805,3 +805,77 @@ void k_pipe_block_put(struct k_pipe *pipe, struct k_mem_block *block,
 				    bytes_to_write, K_FOREVER);
 }
 #endif
+
+size_t z_impl_k_pipe_read_avail(struct k_pipe *pipe)
+{
+	size_t res;
+	k_spinlock_key_t key;
+
+	/* Buffer and size are fixed. No need to spin. */
+	if (pipe->buffer == NULL || pipe->size == 0) {
+		res = 0;
+		goto out;
+	}
+
+	key = k_spin_lock(&pipe->lock);
+
+	if (pipe->read_index == pipe->write_index) {
+		res = pipe->bytes_used;
+	} else if (pipe->read_index < pipe->write_index) {
+		res = pipe->write_index - pipe->read_index;
+	} else {
+		res = pipe->size - (pipe->read_index - pipe->write_index);
+	}
+
+	k_spin_unlock(&pipe->lock, key);
+
+out:
+	return res;
+}
+
+#ifdef CONFIG_USERSPACE
+size_t z_vrfy_k_pipe_read_avail(struct k_pipe *pipe)
+{
+	Z_OOPS(Z_SYSCALL_OBJ(pipe, K_OBJ_PIPE));
+
+	return z_impl_k_pipe_read_avail(pipe);
+}
+#include <syscalls/k_pipe_read_avail_mrsh.c>
+#endif
+
+size_t z_impl_k_pipe_write_avail(struct k_pipe *pipe)
+{
+	size_t res;
+	k_spinlock_key_t key;
+
+	/* Buffer and size are fixed. No need to spin. */
+	if (pipe->buffer == NULL || pipe->size == 0) {
+		res = 0;
+		goto out;
+	}
+
+	key = k_spin_lock(&pipe->lock);
+
+	if (pipe->write_index == pipe->read_index) {
+		res = pipe->size - pipe->bytes_used;
+	} else if (pipe->write_index < pipe->read_index) {
+		res = pipe->read_index - pipe->write_index;
+	} else {
+		res = pipe->size - (pipe->write_index - pipe->read_index);
+	}
+
+	k_spin_unlock(&pipe->lock, key);
+
+out:
+	return res;
+}
+
+#ifdef CONFIG_USERSPACE
+size_t z_vrfy_k_pipe_write_avail(struct k_pipe *pipe)
+{
+	Z_OOPS(Z_SYSCALL_OBJ(pipe, K_OBJ_PIPE));
+
+	return z_impl_k_pipe_write_avail(pipe);
+}
+#include <syscalls/k_pipe_write_avail_mrsh.c>
+#endif