[sysprof] capture: add sendfile() fallback

[Christian Hergert <chergert src gnome org>]

commit 0580b4ef0d4056e814cb53dc903294224b00bc53
Author: Christian Hergert <chergert redhat com>
Date:   Mon May 6 16:20:14 2019 -0700

    capture: add sendfile() fallback
    
    We want the capture format to be usable on systems other than
    Linux so that it can be used in places like GTK. To do this,
    we need a sendfile() fallback that can be portable/useful on
    those systems.
    
    FreeBSD has sendfile(), but the semantics differ slightly. This
    implementation will walk up to the nearest page size and then
    do page aligned pread()/write() which is likely good enough of
    an implementation anyway.

 lib/capture/sp-capture-util-private.h | 102 ++++++++++++++++++++++++++++++++++
 1 file changed, 102 insertions(+)
---
diff --git a/lib/capture/sp-capture-util-private.h b/lib/capture/sp-capture-util-private.h
new file mode 100644
index 0000000..8a4f40d
--- /dev/null
+++ b/lib/capture/sp-capture-util-private.h
@@ -0,0 +1,102 @@
+/* sp-capture-util-private.h
+ *
+ * Copyright © 2019 Christian Hergert <chergert redhat com>
+ *
+ * This file is free software; you can redistribute it and/or modify it under
+ * the terms of the GNU Lesser General Public License as published by the Free
+ * Software Foundation; either version 2 of the License, or (at your option)
+ * any later version.
+ *
+ * This file is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
+ * License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef SP_CAPTURE_UTIL_PRIVATE_H
+#define SP_CAPTURE_UTIL_PRIVATE_H
+
+#include <glib.h>
+
+#ifdef __linux__
+# include <sys/sendfile.h>
+#endif
+#include <errno.h>
+#include <unistd.h>
+
+#ifdef __linux__
+# define _sp_sendfile sendfile
+#else
+static inline gssize
+_sp_sendfile (gint     out_fd,
+              gint     in_fd,
+              goffset *offset,
+              gsize    count)
+{
+  gssize total = 0;
+  goffset wpos = 0;
+  goffset rpos = 0;
+
+  errno = 0;
+
+  if (offset != NULL && *offset > 0)
+    wpos = rpos = *offset;
+
+  while (count > 0)
+    {
+      guint8 buf[4096*4];
+      gssize n_written = 0;
+      gssize n_read;
+      goffset off = 0;
+      gsize to_read;
+
+      /* Try to page align */
+      if ((rpos % 4096) != 0)
+        to_read = 4096 - rpos;
+      else
+        to_read = sizeof buf;
+
+      if (to_read > count)
+        to_read = count;
+
+      errno = 0;
+      n_read = pread (in_fd, buf, to_read, rpos);
+
+      if (n_read <= 0)
+        return -1;
+
+      g_assert (count >= n_read);
+
+      count -= n_read;
+      rpos += n_read;
+
+      while (wpos < rpos)
+        {
+          g_assert (off < sizeof buf);
+
+          errno = 0;
+          n_written = write (out_fd, &buf[off], rpos - wpos);
+
+          if (n_written <= 0)
+            return -1;
+
+          wpos += n_written;
+          off += n_written;
+          total += n_written;
+        }
+    }
+
+  g_assert (count == 0);
+
+  if (offset != NULL)
+    *offset = rpos;
+
+  errno = 0;
+  return total;
+}
+#endif
+
+#endif /* SP_CAPTURE_UTIL_PRIVATE_H */