thread_with_file: Lift from bcachefstime_stats_twf

thread_with_file and thread_with_stdio are abstractions for connecting
kthreads to file descriptors, which is handy for all sorts of things -
the running kthread has its lifetime connected to the file descriptor,
which means an asynchronous job running in the kernel can easily exit in
response to a ctrl-c, and the file descriptor also provides a
communications channel.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

2 files changed, 104 insertions, 0 deletions

diff --git a/include/linux/thread_with_file.h b/include/linux/thread_with_file.h
new file mode 100644
index 000000000000..cf44337af3e9
--- /dev/null
+++ b/include/linux/thread_with_file.h
@@ -0,0 +1,79 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * (C) 2022-2024 Kent Overstreet <kent.overstreet@linux.dev>
+ */
+#ifndef _LINUX_THREAD_WITH_FILE_H
+#define _LINUX_THREAD_WITH_FILE_H
+
+#include <linux/thread_with_file_types.h>
+
+/*
+ * Thread with file: Run a kthread and connect it to a file descriptor, so that
+ * it can be interacted with via fd read/write methods and closing the file
+ * descriptor stops the kthread.
+ *
+ * We have two different APIs:
+ *
+ * thread_with_file, the low level version.
+ * You get to define the full file_operations, including your release function,
+ * which means that you must call thread_with_file_exit() from your
+ * .release method
+ *
+ * thread_with_stdio, the higher level version
+ * This implements full piping of input and output, including .poll.
+ *
+ * Notes on behaviour:
+ *  - kthread shutdown behaves like writing or reading from a pipe that has been
+ *    closed
+ *  - Input and output buffers are 4096 bytes, although buffers may in some
+ *    situations slightly exceed that limit so as to avoid chopping off a
+ *    message in the middle in nonblocking mode.
+ *  - Input/output buffers are lazily allocated, with GFP_NOWAIT allocations -
+ *    should be fine but might change in future revisions.
+ *  - Output buffer may grow past 4096 bytes to deal with messages that are
+ *    bigger than 4096 bytes
+ *  - Writing may be done blocking or nonblocking; in nonblocking mode, we only
+ *    drop entire messages.
+ *
+ * To write, use stdio_redirect_printf()
+ * To read, use stdio_redirect_read() or stdio_redirect_readline()
+ */
+
+struct task_struct;
+
+struct thread_with_file {
+	struct task_struct	*task;
+	int			ret;
+	bool			done;
+};
+
+void thread_with_file_exit(struct thread_with_file *);
+int run_thread_with_file(struct thread_with_file *,
+			 const struct file_operations *,
+			 int (*fn)(void *));
+
+struct thread_with_stdio;
+
+struct thread_with_stdio_ops {
+	void (*exit)(struct thread_with_stdio *);
+	int (*fn)(struct thread_with_stdio *);
+	long (*unlocked_ioctl)(struct thread_with_stdio *, unsigned int, unsigned long);
+};
+
+struct thread_with_stdio {
+	struct thread_with_file	thr;
+	struct stdio_redirect	stdio;
+	const struct thread_with_stdio_ops	*ops;
+};
+
+int run_thread_with_stdio(struct thread_with_stdio *,
+			  const struct thread_with_stdio_ops *);
+int run_thread_with_stdout(struct thread_with_stdio *,
+			  const struct thread_with_stdio_ops *);
+int stdio_redirect_read(struct stdio_redirect *, char *, size_t);
+int stdio_redirect_readline(struct stdio_redirect *, char *, size_t);
+
+__printf(3, 0) ssize_t stdio_redirect_vprintf(struct stdio_redirect *, bool, const char *, va_list);
+__printf(3, 4) ssize_t stdio_redirect_printf(struct stdio_redirect *, bool, const char *, ...);
+
+#endif /* _LINUX_THREAD_WITH_FILE_H */
diff --git a/include/linux/thread_with_file_types.h b/include/linux/thread_with_file_types.h
new file mode 100644
index 000000000000..98d0ad125322
--- /dev/null
+++ b/include/linux/thread_with_file_types.h
@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_THREAD_WITH_FILE_TYPES_H
+#define _LINUX_THREAD_WITH_FILE_TYPES_H
+
+#include <linux/darray_types.h>
+#include <linux/spinlock_types.h>
+#include <linux/wait.h>
+
+struct stdio_buf {
+	spinlock_t		lock;
+	wait_queue_head_t	wait;
+	darray_char		buf;
+};
+
+struct stdio_redirect {
+	struct stdio_buf	input;
+	struct stdio_buf	output;
+
+	spinlock_t		input_lock;
+	wait_queue_head_t	input_wait;
+	darray_char		input_buf;
+	bool			done;
+};
+
+#endif /* _LINUX_THREAD_WITH_FILE_TYPES_H */