1 files changed, 611 insertions, 0 deletions
diff --git a/src/tracefs-record.c b/src/tracefs-record.c
new file mode 100644
index 0000000..b078c86
--- /dev/null
+++ b/src/tracefs-record.c
@@ -0,0 +1,611 @@
+// SPDX-License-Identifier: LGPL-2.1
+/*
+ * Copyright (C) 2022 Google Inc, Steven Rostedt <rostedt@goodmis.org>
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <dirent.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <errno.h>
+#include <sys/stat.h>
+#include <sys/ioctl.h>
+#include <sys/select.h>
+
+#include <kbuffer.h>
+
+#include "tracefs.h"
+#include "tracefs-local.h"
+
+enum {
+	TC_STOP			= 1 << 0,   /* Stop reading */
+	TC_PERM_NONBLOCK	= 1 << 1,   /* read is always non blocking */
+	TC_NONBLOCK		= 1 << 2,   /* read is non blocking */
+};
+
+struct tracefs_cpu {
+	int		fd;
+	int		flags;
+	int		nfds;
+	int		ctrl_pipe[2];
+	int		splice_pipe[2];
+	int		pipe_size;
+	int		subbuf_size;
+	int		buffered;
+	int		splice_read_flags;
+};
+
+/**
+ * tracefs_cpu_alloc_fd - create a tracefs_cpu instance for an existing fd
+ * @fd: The file descriptor to attach the tracefs_cpu to
+ * @subbuf_size: The expected size to read the subbuffer with
+ * @nonblock: If true, the file will be opened in O_NONBLOCK mode
+ *
+ * Return a descriptor that can read the tracefs trace_pipe_raw file
+ * that is associated with the given @fd and must be read in @subbuf_size.
+ *
+ * Returns NULL on error.
+ */
+struct tracefs_cpu *
+tracefs_cpu_alloc_fd(int fd, int subbuf_size, bool nonblock)
+{
+	struct tracefs_cpu *tcpu;
+	int mode = O_RDONLY;
+	int ret;
+
+	tcpu = calloc(1, sizeof(*tcpu));
+	if (!tcpu)
+		return NULL;
+
+	if (nonblock) {
+		mode |= O_NONBLOCK;
+		tcpu->flags |= TC_NONBLOCK | TC_PERM_NONBLOCK;
+	}
+
+	tcpu->splice_pipe[0] = -1;
+	tcpu->splice_pipe[1] = -1;
+
+	tcpu->fd = fd;
+
+	tcpu->subbuf_size = subbuf_size;
+
+	if (tcpu->flags & TC_PERM_NONBLOCK) {
+		tcpu->ctrl_pipe[0] = -1;
+		tcpu->ctrl_pipe[1] = -1;
+	} else {
+		/* ctrl_pipe is used to break out of blocked reads */
+		ret = pipe(tcpu->ctrl_pipe);
+		if (ret < 0)
+			goto fail;
+		if (tcpu->ctrl_pipe[0] > tcpu->fd)
+			tcpu->nfds = tcpu->ctrl_pipe[0] + 1;
+		else
+			tcpu->nfds = tcpu->fd + 1;
+	}
+
+	return tcpu;
+ fail:
+	free(tcpu);
+	return NULL;
+}
+
+/**
+ * tracefs_cpu_open - open an instance raw trace file
+ * @instance: the instance (NULL for toplevel) of the cpu raw file to open
+ * @cpu: The CPU that the raw trace file is associated with
+ * @nonblock: If true, the file will be opened in O_NONBLOCK mode
+ *
+ * Return a descriptor that can read the tracefs trace_pipe_raw file
+ * for a give @cpu in a given @instance.
+ *
+ * Returns NULL on error.
+ */
+struct tracefs_cpu *
+tracefs_cpu_open(struct tracefs_instance *instance, int cpu, bool nonblock)
+{
+	struct tracefs_cpu *tcpu;
+	struct tep_handle *tep;
+	char path[128];
+	char *buf;
+	int mode = O_RDONLY;
+	int subbuf_size;
+	int len;
+	int ret;
+	int fd;
+
+	if (nonblock)
+		mode |= O_NONBLOCK;
+
+	sprintf(path, "per_cpu/cpu%d/trace_pipe_raw", cpu);
+
+	fd = tracefs_instance_file_open(instance, path, mode);
+	if (fd < 0)
+		return NULL;
+
+	tep = tep_alloc();
+	if (!tep)
+		goto fail;
+
+	/* Get the size of the page */
+	buf = tracefs_instance_file_read(NULL, "events/header_page", &len);
+	if (!buf)
+		goto fail;
+
+	ret = tep_parse_header_page(tep, buf, len, sizeof(long));
+	free(buf);
+	if (ret < 0)
+		goto fail;
+
+	subbuf_size = tep_get_sub_buffer_size(tep);
+	tep_free(tep);
+	tep = NULL;
+
+	tcpu = tracefs_cpu_alloc_fd(fd, subbuf_size, nonblock);
+	if (!tcpu)
+		goto fail;
+
+	return tcpu;
+ fail:
+	tep_free(tep);
+	close(fd);
+	return NULL;
+}
+
+static void close_fd(int fd)
+{
+	if (fd < 0)
+		return;
+	close(fd);
+}
+
+/**
+ * tracefs_cpu_free_fd - clean up the tracefs_cpu descriptor
+ * @tcpu: The descriptor created with tracefs_cpu_alloc_fd()
+ *
+ * Closes all the internal file descriptors that were opened by
+ * tracefs_cpu_alloc_fd(), and frees the descriptor.
+ */
+void tracefs_cpu_free_fd(struct tracefs_cpu *tcpu)
+{
+	close_fd(tcpu->ctrl_pipe[0]);
+	close_fd(tcpu->ctrl_pipe[1]);
+	close_fd(tcpu->splice_pipe[0]);
+	close_fd(tcpu->splice_pipe[1]);
+
+	free(tcpu);
+}
+
+/**
+ * tracefs_cpu_close - clean up and close a raw trace descriptor
+ * @tcpu: The descriptor created with tracefs_cpu_open()
+ *
+ * Closes all the file descriptors associated to the trace_pipe_raw
+ * opened by tracefs_cpu_open().
+ */
+void tracefs_cpu_close(struct tracefs_cpu *tcpu)
+{
+	if (!tcpu)
+		return;
+
+	close(tcpu->fd);
+	tracefs_cpu_free_fd(tcpu);
+}
+
+/**
+ * tracefs_cpu_read_size - Return the size of the sub buffer
+ * @tcpu: The descriptor that holds the size of the sub buffer
+ *
+ * A lot of the functions that read the data from the trace_pipe_raw
+ * expect the caller to have allocated enough space to store a full
+ * subbuffer. Calling this function is a requirement to do so.
+ */
+int tracefs_cpu_read_size(struct tracefs_cpu *tcpu)
+{
+	if (!tcpu)
+		return -1;
+	return tcpu->subbuf_size;
+}
+
+static void set_nonblock(struct tracefs_cpu *tcpu)
+{
+	long flags;
+
+	if (tcpu->flags & TC_NONBLOCK)
+		return;
+
+	flags = fcntl(tcpu->fd, F_GETFL);
+	fcntl(tcpu->fd, F_SETFL, flags | O_NONBLOCK);
+	tcpu->flags |= TC_NONBLOCK;
+}
+
+static void unset_nonblock(struct tracefs_cpu *tcpu)
+{
+	long flags;
+
+	if (!(tcpu->flags & TC_NONBLOCK))
+		return;
+
+	flags = fcntl(tcpu->fd, F_GETFL);
+	flags &= ~O_NONBLOCK;
+	fcntl(tcpu->fd, F_SETFL, flags);
+	tcpu->flags &= ~TC_NONBLOCK;
+}
+
+/*
+ * If set to blocking mode, block until the watermark has been
+ * reached, or the control has said to stop. If the contol is
+ * set, then nonblock will be set to true on the way out.
+ */
+static int wait_on_input(struct tracefs_cpu *tcpu, bool nonblock)
+{
+	fd_set rfds;
+	int ret;
+
+	if (tcpu->flags & TC_PERM_NONBLOCK)
+		return 1;
+
+	if (nonblock) {
+		set_nonblock(tcpu);
+		return 1;
+	} else {
+		unset_nonblock(tcpu);
+	}
+
+	FD_ZERO(&rfds);
+	FD_SET(tcpu->fd, &rfds);
+	FD_SET(tcpu->ctrl_pipe[0], &rfds);
+
+	ret = select(tcpu->nfds, &rfds, NULL, NULL, NULL);
+
+	/* Let the application decide what to do with signals and such */
+	if (ret < 0)
+		return ret;
+
+	if (FD_ISSET(tcpu->ctrl_pipe[0], &rfds)) {
+		/* Flush the ctrl pipe */
+		read(tcpu->ctrl_pipe[0], &ret, 1);
+
+		/* Make nonblock as it is now stopped */
+		set_nonblock(tcpu);
+		/* Permanently set unblock */
+		tcpu->flags |= TC_PERM_NONBLOCK;
+	}
+
+	return FD_ISSET(tcpu->fd, &rfds);
+}
+
+/**
+ * tracefs_cpu_read - read from the raw trace file
+ * @tcpu: The descriptor representing the raw trace file
+ * @buffer: Where to read into (must be at least the size of the subbuffer)
+ * @nonblock: Hint to not block on the read if there's no data.
+ *
+ * Reads the trace_pipe_raw files associated to @tcpu into @buffer.
+ * @buffer must be at least the size of the sub buffer of the ring buffer,
+ * which is returned by tracefs_cpu_read_size().
+ *
+ * If @nonblock is set, and there's no data available, it will return
+ * immediately. Otherwise depending on how @tcpu was opened, it will
+ * block. If @tcpu was opened with nonblock set, then this @nonblock
+ * will make no difference.
+ *
+ * Returns the amount read or -1 on error.
+ */
+int tracefs_cpu_read(struct tracefs_cpu *tcpu, void *buffer, bool nonblock)
+{
+	int ret;
+
+	/*
+	 * If nonblock is set, then the wait_on_input() will return
+	 * immediately, if there's nothing in the buffer, with
+	 * ret == 0.
+	 */
+	ret = wait_on_input(tcpu, nonblock);
+	if (ret <= 0)
+		return ret;
+
+	ret = read(tcpu->fd, buffer, tcpu->subbuf_size);
+
+	/* It's OK if there's no data to read */
+	if (ret < 0 && errno == EAGAIN) {
+		/* Reset errno */
+		errno = 0;
+		ret = 0;
+	}
+
+	return ret;
+}
+
+static int init_splice(struct tracefs_cpu *tcpu)
+{
+	int ret;
+
+	if (tcpu->splice_pipe[0] >= 0)
+		return 0;
+
+	ret = pipe(tcpu->splice_pipe);
+	if (ret < 0)
+		return ret;
+
+	ret = fcntl(tcpu->splice_pipe[0], F_GETPIPE_SZ, &tcpu->pipe_size);
+	/*
+	 * F_GETPIPE_SZ was introduced in 2.6.35, ftrace was introduced
+	 * in 2.6.31. If we are running on an older kernel, just fall
+	 * back to using subbuf_size for splice(). It could also return
+	 * the size of the pipe and not set pipe_size.
+	 */
+	if (ret > 0 && !tcpu->pipe_size)
+		tcpu->pipe_size = ret;
+	else if (ret < 0)
+		tcpu->pipe_size = tcpu->subbuf_size;
+
+	tcpu->splice_read_flags = SPLICE_F_MOVE;
+	if (tcpu->flags & TC_NONBLOCK)
+		tcpu->splice_read_flags |= SPLICE_F_NONBLOCK;
+
+	return 0;
+}
+
+/**
+ * tracefs_cpu_buffered_read - Read the raw trace data buffering through a pipe
+ * @tcpu: The descriptor representing the raw trace file
+ * @buffer: Where to read into (must be at least the size of the subbuffer)
+ * @nonblock: Hint to not block on the read if there's no data.
+ *
+ * This is basically the same as tracefs_cpu_read() except that it uses
+ * a pipe through splice to buffer reads. This will batch reads keeping
+ * the reading from the ring buffer less intrusive to the system, as
+ * just reading all the time can cause quite a disturbance.
+ *
+ * Note, one difference between this and tracefs_cpu_read() is that it
+ * will read only in sub buffer pages. If the ring buffer has not filled
+ * a page, then it will not return anything, even with @nonblock set.
+ * Calls to tracefs_cpu_flush() should be done to read the rest of
+ * the file at the end of the trace.
+ *
+ * Returns the amount read or -1 on error.
+ */
+int tracefs_cpu_buffered_read(struct tracefs_cpu *tcpu, void *buffer, bool nonblock)
+{
+	int mode = SPLICE_F_MOVE;
+	int ret;
+
+	if (tcpu->buffered < 0)
+		tcpu->buffered = 0;
+
+	if (tcpu->buffered)
+		goto do_read;
+
+	ret = wait_on_input(tcpu, nonblock);
+	if (ret <= 0)
+		return ret;
+
+	if (tcpu->flags & TC_NONBLOCK)
+		mode |= SPLICE_F_NONBLOCK;
+
+	ret = init_splice(tcpu);
+	if (ret < 0)
+		return ret;
+
+	ret = splice(tcpu->fd, NULL, tcpu->splice_pipe[1], NULL,
+		     tcpu->pipe_size, mode);
+	if (ret <= 0)
+		return ret;
+
+	tcpu->buffered = ret;
+
+ do_read:
+	ret = read(tcpu->splice_pipe[0], buffer, tcpu->subbuf_size);
+	if (ret > 0)
+		tcpu->buffered -= ret;
+	return ret;
+}
+
+/**
+ * tracefs_cpu_stop - Stop a blocked read of the raw tracing file
+ * @tcpu: The descriptor representing the raw trace file
+ *
+ * This will attempt to unblock a task blocked on @tcpu reading it.
+ * On older kernels, it may not do anything for the pipe reads, as
+ * older kernels do not wake up tasks waiting on the ring buffer.
+ *
+ * Returns 0 if the tasks reading the raw tracing file does not
+ * need a nudge.
+ *
+ * Returns 1 if that tasks may need a nudge (send a signal).
+ *
+ * Returns negative on error.
+ */
+int tracefs_cpu_stop(struct tracefs_cpu *tcpu)
+{
+	int ret = 1;
+
+	if (tcpu->flags & TC_PERM_NONBLOCK)
+		return 0;
+
+	ret = write(tcpu->ctrl_pipe[1], &ret, 1);
+	if (ret < 0)
+		return ret;
+
+	/* Calling ioctl() on recent kernels will wake up the waiters */
+	ret = ioctl(tcpu->fd, 0);
+	if (ret < 0)
+		ret = 1;
+	else
+		ret = 0;
+
+	set_nonblock(tcpu);
+
+	return ret;
+}
+
+/**
+ * tracefs_cpu_flush - Finish out and read the rest of the raw tracing file
+ * @tcpu: The descriptor representing the raw trace file
+ * @buffer: Where to read into (must be at least the size of the subbuffer)
+ *
+ * Reads the trace_pipe_raw file associated by the @tcpu and puts it
+ * into @buffer, which must be the size of the sub buffer which is retrieved.
+ * by tracefs_cpu_read_size(). This should be called at the end of tracing
+ * to get the rest of the data.
+ *
+ * This will set the file descriptor for reading to non-blocking mode.
+ *
+ * Returns the number of bytes read, or negative on error.
+ */
+int tracefs_cpu_flush(struct tracefs_cpu *tcpu, void *buffer)
+{
+	int ret;
+
+	/* Make sure that reading is now non blocking */
+	set_nonblock(tcpu);
+
+	if (tcpu->buffered < 0)
+		tcpu->buffered = 0;
+
+	if (tcpu->buffered) {
+		ret = read(tcpu->splice_pipe[0], buffer, tcpu->subbuf_size);
+		if (ret > 0)
+			tcpu->buffered -= ret;
+		return ret;
+	}
+
+	ret = read(tcpu->fd, buffer, tcpu->subbuf_size);
+	if (ret > 0 && tcpu->buffered)
+		tcpu->buffered -= ret;
+
+	/* It's OK if there's no data to read */
+	if (ret < 0 && errno == EAGAIN) {
+		/* Reset errno */
+		errno = 0;
+		ret = 0;
+	}
+
+	return ret;
+}
+
+/**
+ * tracefs_cpu_flush_write - Finish out and read the rest of the raw tracing file
+ * @tcpu: The descriptor representing the raw trace file
+ * @wfd: The write file descriptor to write the data to
+ *
+ * Reads the trace_pipe_raw file associated by the @tcpu and writes it to
+ * @wfd. This should be called at the end of tracing to get the rest of the data.
+ *
+ * Returns the number of bytes written, or negative on error.
+ */
+int tracefs_cpu_flush_write(struct tracefs_cpu *tcpu, int wfd)
+{
+	char buffer[tcpu->subbuf_size];
+	int ret;
+
+	ret = tracefs_cpu_flush(tcpu, buffer);
+	if (ret > 0)
+		ret = write(wfd, buffer, ret);
+
+	/* It's OK if there's no data to read */
+	if (ret < 0 && errno == EAGAIN)
+		ret = 0;
+
+	return ret;
+}
+
+/**
+ * tracefs_cpu_write - Write the raw trace file into a file descriptor
+ * @tcpu: The descriptor representing the raw trace file
+ * @wfd: The write file descriptor to write the data to
+ * @nonblock: Hint to not block on the read if there's no data.
+ *
+ * This will pipe the data from the trace_pipe_raw file associated with @tcpu
+ * into the @wfd file descriptor. If @nonblock is set, then it will not
+ * block on if there's nothing to write. Note, it will only write sub buffer
+ * size data to @wfd. Calls to tracefs_cpu_flush_write() are needed to
+ * write out the rest.
+ *
+ * Returns the number of bytes read or negative on error.
+ */
+int tracefs_cpu_write(struct tracefs_cpu *tcpu, int wfd, bool nonblock)
+{
+	char buffer[tcpu->subbuf_size];
+	int mode = SPLICE_F_MOVE;
+	int tot_write = 0;
+	int tot;
+	int ret;
+
+	ret = wait_on_input(tcpu, nonblock);
+	if (ret <= 0)
+		return ret;
+
+	if (tcpu->flags & TC_NONBLOCK)
+		mode |= SPLICE_F_NONBLOCK;
+
+	ret = init_splice(tcpu);
+	if (ret < 0)
+		return ret;
+
+	tot = splice(tcpu->fd, NULL, tcpu->splice_pipe[1], NULL,
+		     tcpu->pipe_size, mode);
+	if (tot < 0)
+		return tot;
+
+	if (tot == 0)
+		return 0;
+
+	ret = splice(tcpu->splice_pipe[0], NULL, wfd, NULL,
+		     tot, SPLICE_F_MOVE | SPLICE_F_NONBLOCK);
+
+	if (ret >= 0)
+		return ret;
+
+	/* Some file systems do not allow splicing, try writing instead */
+	do {
+		int r = tcpu->subbuf_size;
+
+		if (r > tot)
+			r = tot;
+
+		ret = read(tcpu->splice_pipe[0], buffer, r);
+		if (ret > 0) {
+			tot -= ret;
+			ret = write(wfd, buffer, ret);
+		}
+		if (ret > 0)
+			tot_write += ret;
+	} while (ret > 0);
+
+	if (ret < 0)
+		return ret;
+
+	return tot_write;
+}
+
+/**
+ * tracefs_cpu_pipe - Write the raw trace file into a pipe descriptor
+ * @tcpu: The descriptor representing the raw trace file
+ * @wfd: The write file descriptor to write the data to (must be a pipe)
+ * @nonblock: Hint to not block on the read if there's no data.
+ *
+ * This will splice directly the file descriptor of the trace_pipe_raw
+ * file to the given @wfd, which must be a pipe. This can also be used
+ * if @tcpu was created with tracefs_cpu_create_fd() where the passed
+ * in @fd there was a pipe, then @wfd does not need to be a pipe.
+ *
+ * Returns the number of bytes read or negative on error.
+ */
+int tracefs_cpu_pipe(struct tracefs_cpu *tcpu, int wfd, bool nonblock)
+{
+	int mode = SPLICE_F_MOVE;
+	int ret;
+
+	ret = wait_on_input(tcpu, nonblock);
+	if (ret <= 0)
+		return ret;
+
+	if (tcpu->flags & TC_NONBLOCK)
+		mode |= SPLICE_F_NONBLOCK;
+
+	ret = splice(tcpu->fd, NULL, wfd, NULL,
+		     tcpu->pipe_size, mode);
+	return ret;
+}