linux-kernel - [PATCH v3 16/18] rtla/trace: Fix I/O handling in save_trace_to

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Message-ID: <20260115163650.118910-17-wander@redhat.com>
Date: Thu, 15 Jan 2026 13:31:59 -0300
From: Wander Lairson Costa <wander@...hat.com>
To: Steven Rostedt <rostedt@...dmis.org>,
	Tomas Glozar <tglozar@...hat.com>,
	Wander Lairson Costa <wander@...hat.com>,
	Ivan Pravdin <ipravdin.official@...il.com>,
	Crystal Wood <crwood@...hat.com>,
	Costa Shulyupin <costa.shul@...hat.com>,
	John Kacur <jkacur@...hat.com>,
	Haiyong Sun <sunhaiyong@...ngson.cn>,
	Tiezhu Yang <yangtiezhu@...ngson.cn>,
	Daniel Wagner <dwagner@...e.de>,
	Daniel Bristot de Oliveira <bristot@...nel.org>,
	linux-trace-kernel@...r.kernel.org (open list:Real-time Linux Analysis (RTLA) tools),
	linux-kernel@...r.kernel.org (open list:Real-time Linux Analysis (RTLA) tools),
	bpf@...r.kernel.org (open list:BPF [MISC]:Keyword:(?:\b|_)bpf(?:\b|_))
Subject: [PATCH v3 16/18] rtla/trace: Fix I/O handling in save_trace_to_file()

The read/write loop in save_trace_to_file() does not correctly handle
errors from the read() and write() system calls. If either call is
interrupted by a signal, it returns -1 with errno set to EINTR, but
the code treats this as a fatal error and aborts the save operation.
Additionally, write() may perform a partial write, returning fewer
bytes than requested, which the code does not handle.

Fix the I/O loop by introducing proper error handling. The return
value of read() is now stored in a ssize_t variable and checked for
errors, with EINTR causing a retry. For write(), an inner loop ensures
all bytes are written, handling both EINTR and partial writes. Error
messages now include strerror() output for better debugging.

This follows the same pattern established in the previous commit that
fixed trace_event_save_hist(), ensuring consistent and robust I/O
handling throughout the trace saving code.

Signed-off-by: Wander Lairson Costa <wander@...hat.com>
---
 tools/tracing/rtla/src/trace.c | 30 +++++++++++++++++++++++-------
 1 file changed, 23 insertions(+), 7 deletions(-)

diff --git a/tools/tracing/rtla/src/trace.c b/tools/tracing/rtla/src/trace.c
index fed3362527b08..8e93b48d33ef8 100644
--- a/tools/tracing/rtla/src/trace.c
+++ b/tools/tracing/rtla/src/trace.c
@@ -73,6 +73,7 @@ int save_trace_to_file(struct tracefs_instance *inst, const char *filename)
 	char buffer[4096];
 	int out_fd, in_fd;
 	int retval = -1;
+	ssize_t n_read;
 
 	if (!inst || !filename)
 		return 0;
@@ -90,15 +91,30 @@ int save_trace_to_file(struct tracefs_instance *inst, const char *filename)
 		goto out_close_in;
 	}
 
-	do {
-		retval = read(in_fd, buffer, sizeof(buffer));
-		if (retval <= 0)
+	for (;;) {
+		n_read = read(in_fd, buffer, sizeof(buffer));
+		if (n_read < 0) {
+			if (errno == EINTR)
+				continue;
+			err_msg("Error reading trace file: %s\n", strerror(errno));
 			goto out_close;
+		}
+		if (n_read == 0)
+			break;
 
-		retval = write(out_fd, buffer, retval);
-		if (retval < 0)
-			goto out_close;
-	} while (retval > 0);
+		ssize_t n_written = 0;
+		while (n_written < n_read) {
+			ssize_t w = write(out_fd, buffer + n_written, n_read - n_written);
+
+			if (w < 0) {
+				if (errno == EINTR)
+					continue;
+				err_msg("Error writing trace file: %s\n", strerror(errno));
+				goto out_close;
+			}
+			n_written += w;
+		}
+	}
 
 	retval = 0;
 out_close:
-- 
2.52.0