libsysprof-profile: use GByteArray for read buffer

That way we aren't relying on the stack for access to buffer data.

src/libsysprof-profile/sysprof-disk-usage.c

@@ -180,10 +180,10 @@ find_device_by_name (Record     *record,
 static DexFuture *
 sysprof_disk_usage_record_fiber (gpointer user_data)
 {
+  g_autoptr(GByteArray) buf = NULL;
   Record *record = user_data;
   SysprofCaptureWriter *writer;
   g_autofd int stat_fd = -1;
-  char buf[4096*4];
   LineReader reader;
   DiskUsage *combined;
   gint64 combined_reads_total = 0;
@@ -194,6 +194,9 @@ sysprof_disk_usage_record_fiber (gpointer user_data)
   g_assert (SYSPROF_IS_RECORDING (record->recording));
   g_assert (DEX_IS_CANCELLABLE (record->cancellable));
 
+  buf = g_byte_array_new ();
+  g_byte_array_set_size (buf, 4096*4);
+
   if (-1 == (stat_fd = open ("/proc/diskstats", O_RDONLY|O_CLOEXEC)))
     return dex_future_new_for_errno (errno);
 
@@ -212,7 +215,7 @@ sysprof_disk_usage_record_fiber (gpointer user_data)
        * recording loop. If cancellation future rejects, then
        * we also break out of our recording loop.
        */
-      read_future = dex_aio_read (NULL, stat_fd, buf, sizeof buf-1, 0);
+      read_future = dex_aio_read (NULL, stat_fd, buf->data, buf->len-1, 0);
       if (!dex_await (dex_future_first (dex_ref (record->cancellable),
                                         dex_ref (read_future),
                                         NULL),
@@ -223,7 +226,7 @@ sysprof_disk_usage_record_fiber (gpointer user_data)
       if (n_read < 0)
         break;
 
-      line_reader_init (&reader, buf, n_read);
+      line_reader_init (&reader, (char *)buf->data, n_read);
       while ((line = line_reader_next (&reader, &line_len)))
         {
           DiskUsage ds = {0};

src/libsysprof-profile/sysprof-memory-usage.c

@@ -171,18 +171,21 @@ record_free (gpointer data)
 static DexFuture *
 sysprof_memory_usage_record_fiber (gpointer user_data)
 {
+  g_autoptr(GByteArray) buf = NULL;
   Record *record = user_data;
   SysprofCaptureWriter *writer;
   g_autoptr(GError) error = NULL;
   SysprofCaptureCounter counters[1];
   MemStat st;
-  char buf[4096];
   guint counter_id;
 
   g_assert (record != NULL);
   g_assert (SYSPROF_IS_RECORDING (record->recording));
   g_assert (DEX_IS_FUTURE (record->cancellable));
 
+  buf = g_byte_array_new ();
+  g_byte_array_set_size (buf, 4096);
+
   writer = _sysprof_recording_writer (record->recording);
 
   if (!mem_stat_open (&st, &error))
@@ -207,7 +210,7 @@ sysprof_memory_usage_record_fiber (gpointer user_data)
 
   for (;;)
     {
-      g_autoptr(DexFuture) read_future = dex_aio_read (NULL, st.stat_fd, buf, sizeof buf-1, 0);
+      g_autoptr(DexFuture) read_future = dex_aio_read (NULL, st.stat_fd, buf->data, buf->len-1, 0);
       gssize n_read;
 
       dex_await (dex_future_first (dex_ref (read_future),
@@ -224,9 +227,9 @@ sysprof_memory_usage_record_fiber (gpointer user_data)
 
       if (n_read > 0)
         {
-          buf[n_read] = 0;
+          buf->data[n_read] = 0;
 
-          mem_stat_parse (&st, buf);
+          mem_stat_parse (&st, (char *)buf->data);
 
           sysprof_capture_writer_set_counters (writer,
                                                SYSPROF_CAPTURE_CURRENT_TIME,

src/libsysprof-profile/sysprof-network-usage.c

@@ -107,7 +107,7 @@ find_device_by_name (GArray     *ar,
 static DexFuture *
 sysprof_network_usage_record_fiber (gpointer user_data)
 {
-  char buf[4096*2];
+  g_autoptr(GByteArray) buf = g_byte_array_new ();
   Record *record = user_data;
   g_autofree SysprofCaptureCounterValue *values = NULL;
   g_autofree guint *ids = NULL;
@@ -128,6 +128,8 @@ sysprof_network_usage_record_fiber (gpointer user_data)
   g_assert (SYSPROF_IS_RECORDING (record->recording));
   g_assert (DEX_IS_FUTURE (record->cancellable));
 
+  g_byte_array_set_size (buf, 4096*2);
+
   writer = _sysprof_recording_writer (record->recording);
 
   if (-1 == (stat_fd = open ("/proc/net/dev", O_RDONLY|O_CLOEXEC)))
@@ -158,12 +160,12 @@ sysprof_network_usage_record_fiber (gpointer user_data)
                                           -1,
                                           ctr, G_N_ELEMENTS (ctr));
 
-  n_read = dex_await_int64 (dex_aio_read (NULL, stat_fd, buf, sizeof buf, 0), &error);
+  n_read = dex_await_int64 (dex_aio_read (NULL, stat_fd, buf->data, buf->len, 0), &error);
   if (n_read <= 0)
     return dex_future_new_for_errno (errno);
 
   lineno = 0;
-  line_reader_init (&reader, buf, n_read);
+  line_reader_init (&reader, (char *)buf->data, n_read);
   while ((line = line_reader_next (&reader, &line_len)))
     {
       DeviceUsage dev = {0};
@@ -229,12 +231,12 @@ sysprof_network_usage_record_fiber (gpointer user_data)
       gint64 combined_rx = 0;
       gint64 combined_tx = 0;
 
-      n_read = dex_await_int64 (dex_aio_read (NULL, stat_fd, buf, sizeof buf, 0), &error);
+      n_read = dex_await_int64 (dex_aio_read (NULL, stat_fd, buf->data, buf->len, 0), &error);
       if (n_read <= 0)
         break;
 
       lineno = 0;
-      line_reader_init (&reader, buf, n_read);
+      line_reader_init (&reader, (char *)buf->data, n_read);
       while ((line = line_reader_next (&reader, &line_len)))
         {
           DeviceUsage *dev;