Eliminate the dependency on kernel pseudo-files when running unit tests

bootstat_log.c

 // Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Implementation of bootstat_log(), part of the Chromium OS 'bootstat'
 // facility.
 
 #include "bootstat.h"
+#include "bootstat_test.h"
 
 #include <stdio.h>
 #include <stddef.h>
 
+#include <sys/fcntl.h>
+#include <sys/param.h>
+#include <sys/stat.h>
 #include <sys/types.h>
-#include <sys/stat.h>
-#include <sys/fcntl.h>
 #include <unistd.h>
 
 //
+// Default path to directory where output statistics will be stored.
+//
+static const char kDefaultOutputDirectoryName[] = "/tmp";
+
+//
 // Paths to the statistics files we snapshot as part of the data to
 // be logged.
 //
-static const char kUptimeStatisticsFileName[] = "/proc/uptime";
+static const char kDefaultUptimeStatisticsFileName[] = "/proc/uptime";
 
 #if defined (__amd64__) || defined (__x86_64__) || defined (__i386__)
-static const char kDiskStatisticsFileName[] = "/sys/block/sda/stat";
+static const char kDefaultDiskStatisticsFileName[] = "/sys/block/sda/stat";
 #elif defined (__arm__)
-static const char kDiskStatisticsFileName[] = "/sys/block/mmcblk0/stat";
+static const char kDefaultDiskStatisticsFileName[] = "/sys/block/mmcblk0/stat";
 #else
 #error "unknown processor type?"
 #endif
 
-
-//
-// Maximum length of any pathname for storing event statistics.
-// Arbitrarily chosen, but see the comment below about truncation.
-//
-#define MAX_STAT_PATH  128
-
-//
-// Output file creation mode:  0666, a.k.a. rw-rw-rw-.
-//
-static const int kFileCreationMode =
-    (S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH);
-
+static const char *output_directory_name = kDefaultOutputDirectoryName;
+static const char *uptime_statistics_file_name =
+    kDefaultUptimeStatisticsFileName;
+static const char *disk_statistics_file_name = kDefaultDiskStatisticsFileName;
 
 static void append_logdata(const char* input_path,
                            const char* output_name_prefix,
                            const char* event_name)
 {
-  char output_path[MAX_STAT_PATH];
+  const mode_t kFileCreationMode =
+      S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH;
+  char output_path[PATH_MAX];
   char buffer[256];
   ssize_t num_read;
   int ifd, ofd;
 
   ifd = open(input_path, O_RDONLY);
   if (ifd < 0) {
     return;
   }
 
   //
-  // We don't want the file name "/tmp/uptime-..." truncated
-  // differently from the the name "/tmp/disk-...", so we truncate
+  // We don't want the file name ".../uptime-..." truncated
+  // differently from the the name ".../disk-...", so we truncate
   // event_name separately using the "%.*s" format.

[kmixter1, 2010/12/06 04:23:52]

Confused by this comment.  Say BOOTSTAT_MAX_EVENT_LEN is 4 and event_name is
abcdefg.  Say sizeof(output_path) == 20.

Result when output_name_prefix="prefix1" would be:
/output/prefix1-abc

Result when output_name_prefix="prefix100000" would be:
/outdir/prefix100000

I guess if is if you assert that something like this holds:

strlen(output_name_prefix) + strlen(output_directory_name) + 2 +
BOOTSTAT_MAX_EVENT_LENGTH <  sizeof(output_path)

   //
-  // We expect that BOOTSTAT_MAX_EVENT_LEN is enough smaller than
-  // MAX_STAT_PATH that output_path will never be truncated.
-  //
-  (void) snprintf(output_path, sizeof(output_path), "/tmp/%s-%.*s",
+  (void) snprintf(output_path, sizeof(output_path), "%s/%s-%.*s",

[kmixter1, 2010/12/06 04:23:52]

space after (void) seems unusual.  Actually I guess we usually use static_cast
explicitly instead of C-style casts, but even with C-style casts we don't
separate with spaces.

+                  output_directory_name,
                   output_name_prefix,
                   BOOTSTAT_MAX_EVENT_LEN - 1, event_name);
   ofd = open(output_path, O_WRONLY | O_APPEND | O_CREAT,
              kFileCreationMode);
   if (ofd < 0) {
     (void) close(ifd);
     return;
   }
 
   while ((num_read = read(ifd, buffer, sizeof(buffer))) > 0) {
     ssize_t num_written = write(ofd, buffer, num_read);
     if (num_written != num_read)
       break;
   }
   (void) close(ofd);
   (void) close(ifd);
 }
 
 
 void bootstat_log(const char* event_name)
 {
-  append_logdata(kUptimeStatisticsFileName, "uptime", event_name);
-  append_logdata(kDiskStatisticsFileName, "disk", event_name);
+  append_logdata(uptime_statistics_file_name, "uptime", event_name);
+  append_logdata(disk_statistics_file_name, "disk", event_name);
 }
+
+
+#ifdef CONFIG_UNIT_TEST
+void bootstat_set_output_directory(const char* dirname)
+{
+  if (dirname != NULL)
+    output_directory_name = dirname;
+  else
+    output_directory_name = kDefaultOutputDirectoryName;
+}
+
+
+void bootstat_set_uptime_file_name(const char* filename)
+{
+  if (filename != NULL)
+    uptime_statistics_file_name = filename;
+  else
+    uptime_statistics_file_name = kDefaultUptimeStatisticsFileName;
+}
+
+
+void bootstat_set_disk_file_name(const char* filename)
+{
+  if (filename != NULL)
+    disk_statistics_file_name = filename;
+  else
+    disk_statistics_file_name = kDefaultDiskStatisticsFileName;
+}
+#endif