From 2c8198c9c2ff82b8ec84737a595a18956378a2f8 Mon Sep 17 00:00:00 2001
From: James Muir <muir.james.a@gmail.com>
Date: Fri, 14 Feb 2025 16:06:42 -0500
Subject: [PATCH 1/2] WIP 1

Share the first part of the Cisco patch authored by Oleksiy Obitotskyy
to fix reading from /proc/schedstat post-switch-root (see #60).

More changes are needed since writing the svg file fails.
---
 src/store.c | 67 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 66 insertions(+), 1 deletion(-)

diff --git a/src/store.c b/src/store.c
index 785d408..e64af79 100644
--- a/src/store.c
+++ b/src/store.c
@@ -20,6 +20,8 @@
   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  ***/
 
+#define _POSIX_C_SOURCE
+
 #include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
@@ -29,6 +31,7 @@
 #include <string.h>
 #include <time.h>
 #include <unistd.h>
+#include <sys/stat.h>
 
 #include "alloc-util.h"
 #include "bootchart.h"
@@ -119,6 +122,68 @@ static void garbage_collect_dead_processes(struct ps_struct *ps_first) {
         }
 }
 
+static int proc_read_full_file(int procfd, const char *fn, char **contents, size_t *size) {
+	int fd = -1;
+	size_t n, l;
+	_cleanup_free_ char *buf = NULL;
+	struct stat st;
+
+	fd = openat(procfd, fn, O_RDONLY|O_CLOEXEC);
+	if (fd < 0)
+		return log_error_errno(errno, "Failed to openat /proc/<>: %m");
+
+	if (fstatat(procfd, fn, &st, 0) < 0)
+		return log_error_errno(errno, "Failed to fstatat /proc/<>: %m");
+
+	n = LINE_MAX;
+	if (S_ISREG(st.st_mode)) {
+
+	        /* Safety check */
+		if (st.st_size > 4*1024*1024)
+			return -E2BIG;
+
+		/* Start with the right file size, but be prepared for
+		 * files from /proc which generally report a file size
+		 * of 0 */
+		if (st.st_size > 0)
+			n = st.st_size;
+	}
+
+	l = 0;
+	for (;;) {
+		char *t;
+		ssize_t k;
+
+		t = realloc(buf, n+1);
+		if (!t)
+			return -ENOMEM;
+
+		buf = t;
+		k = pread(fd, buf + l, n - l, l);
+
+		if (k < 0)
+			return log_error_errno(errno, "Failed to pread /proc/<>: %m");
+		if (k == 0)
+			break;
+
+		l += k;
+		n *= 2;
+
+		/* Safety check */
+		if (n > 4*1024*1024)
+			return -E2BIG;
+	}
+
+	buf[l] = 0;
+	*contents = buf;
+	buf = NULL; /* do not free */
+
+	if (size)
+		*size = l;
+
+	safe_close(fd);
+	return 0;
+}
 
 int log_sample(DIR *proc,
                int sample,
@@ -189,7 +254,7 @@ int log_sample(DIR *proc,
         }
 
         /* Parse "/proc/schedstat" for overall CPU utilization */
-        r = read_full_file("/proc/schedstat", &buf_schedstat, NULL);
+        r = proc_read_full_file(procfd, "schedstat", &buf_schedstat, NULL);
         if (r < 0)
             return log_error_errno(r, "Unable to read schedstat: %m");
 

From 3f1dccd4d03373504a3a722bbcc63198d16fa027 Mon Sep 17 00:00:00 2001
From: James Muir <muir.james.a@gmail.com>
Date: Fri, 21 Feb 2025 08:17:15 -0500
Subject: [PATCH 2/2] use fstat(), include filename in error messages.

---
 src/store.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/store.c b/src/store.c
index e64af79..9670042 100644
--- a/src/store.c
+++ b/src/store.c
@@ -130,10 +130,10 @@ static int proc_read_full_file(int procfd, const char *fn, char **contents, size
 
 	fd = openat(procfd, fn, O_RDONLY|O_CLOEXEC);
 	if (fd < 0)
-		return log_error_errno(errno, "Failed to openat /proc/<>: %m");
+		return log_error_errno(errno, "Failed to openat /proc/%s: %m", fn);
 
-	if (fstatat(procfd, fn, &st, 0) < 0)
-		return log_error_errno(errno, "Failed to fstatat /proc/<>: %m");
+	if (fstat(fd, &st) < 0)
+		return log_error_errno(errno, "Failed to fstat /proc/%s: %m", fn);
 
 	n = LINE_MAX;
 	if (S_ISREG(st.st_mode)) {
@@ -162,7 +162,7 @@ static int proc_read_full_file(int procfd, const char *fn, char **contents, size
 		k = pread(fd, buf + l, n - l, l);
 
 		if (k < 0)
-			return log_error_errno(errno, "Failed to pread /proc/<>: %m");
+			return log_error_errno(errno, "Failed to pread /proc/%s: %m", fn);
 		if (k == 0)
 			break;