Re: [PATCH v10 3/4] tools/mm: add page_owner_filter userspace tool

[Lance Yang]

On Thu, Jun 18, 2026 at 11:57:49AM +0800, Zhen Ni wrote:
[...]
>+	/* Read and display filtered output */
>+	ret = 0;
>+	while ((ret = read(fd, buf, sizeof(buf))) > 0) {
>+		size_t written = fwrite(buf, 1, ret, output);
>+
>+		if (written != (size_t)ret) {
>+			if (errno == EPIPE) {

Hmm ... does this work without handling SIGPIPE first?

With something like:

$ ./page_owner_filter -m handle | head

The writer can be killed by SIGPIPE before fwrite() returns EPIPE no?
so this branch would usually not be reached ...

>+				/* Pipe closed, treat as success */
>+				ret = 0;
>+				goto out;
>+			}
>+			perror("write output");
>+			ret = -1;
>+			goto out;
>+		}
>+	}
>+
>+	if (ret < 0) {
>+		perror("read page_owner");
>+		goto out;
>+	}
>+
>+	if (fflush(output)) {

fflush() can also be where the broken pipe is reported, but still treats
EPIPE as an error ...

Shouldn't we ignore/handle SIGPIPE and treat EPIPE from both fwrite()
and fflush() as succes?

Cheers, Lance

>+		perror("flush output");
>+		ret = -1;
>+	}
>+
>+out:
>+	close(fd);
>+	if (output != stdout)
>+		fclose(output);
>+	return ret < 0 ? 1 : 0;
>+}
>-- 
>2.20.1
>
>