[vte/vte-next] [stream-file] Bug 637275 - Use pread/pwrite() if available

[Behdad Esfahbod <behdad src gnome org>]

commit 478c0671b12fc40d061218e49fc15cbf2ffc41bd
Author: Behdad Esfahbod <behdad behdad org>
Date:   Fri Sep 27 16:04:36 2013 -0400

    [stream-file] Bug 637275 - Use pread/pwrite() if available
    
    Turns syscalls in half.

 configure.in         |    3 +++
 src/vtestream-file.h |   42 ++++++++++++++++++++++++++++++++----------
 2 files changed, 35 insertions(+), 10 deletions(-)
---
diff --git a/configure.in b/configure.in
index b1c59cb..72b282c 100644
--- a/configure.in
+++ b/configure.in
@@ -229,6 +229,9 @@ AC_HEADER_TIOCGWINSZ
 # Check for PTY handling functions.
 AC_CHECK_FUNCS([cfmakeraw fork setsid setpgid getpgid getpt grantpt unlockpt posix_openpt ptsname ptsname_r 
tcgetattr tcsetattr])
 
+# Misc I/O routines.
+AC_CHECK_FUNCS([pread pwrite])
+
 # Pull in the right libraries for various functions which might not be
 # bundled into an exploded libc.
 AC_CHECK_FUNC(socket,[have_socket=1],AC_CHECK_LIB(socket,socket,[have_socket=1; LIBS="$LIBS -lsocket"]))
diff --git a/src/vtestream-file.h b/src/vtestream-file.h
index 28f5281..8a0e57c 100644
--- a/src/vtestream-file.h
+++ b/src/vtestream-file.h
@@ -24,8 +24,31 @@
 
 #include <gio/gunixinputstream.h>
 
+
+#ifndef HAVE_PREAD
+#define pread _pread
+static gsize
+pread (int fd, char *data, gsize len, gsize offset)
+{
+  if (-1 == lseek (fd, offset, SEEK_SET))
+    return -1;
+  return read (fd, data, len);
+}
+#endif
+
+#ifndef HAVE_PWRITE
+#define pwrite _pwrite
 static gsize
-_xread (int fd, char *data, gsize len)
+pwrite (int fd, char *data, gsize len, gsize offset)
+{
+  if (-1 == lseek (fd, offset, SEEK_SET))
+    return -1;
+  return write (fd, data, len);
+}
+#endif
+
+static gsize
+_xpread (int fd, char *data, gsize len, gsize offset)
 {
        gsize ret, total = 0;
 
@@ -33,7 +56,7 @@ _xread (int fd, char *data, gsize len)
                return 0;
 
        while (len) {
-               ret = read (fd, data, len);
+               ret = pread (fd, data, len, offset);
                if (G_UNLIKELY (ret == (gsize) -1)) {
                        if (errno == EINTR)
                                continue;
@@ -44,20 +67,21 @@ _xread (int fd, char *data, gsize len)
                        break;
                data += ret;
                len -= ret;
+               offset += ret;
                total += ret;
        }
        return total;
 }
 
 static void
-_xwrite (int fd, const char *data, gsize len)
+_xpwrite (int fd, const char *data, gsize len, gsize offset)
 {
        gsize ret;
 
        g_assert (fd || !len);
 
        while (len) {
-               ret = write (fd, data, len);
+               ret = pwrite (fd, data, len, offset);
                if (G_UNLIKELY (ret == (gsize) -1)) {
                        if (errno == EINTR)
                                continue;
@@ -68,6 +92,7 @@ _xwrite (int fd, const char *data, gsize len)
                        break;
                data += ret;
                len -= ret;
+               offset += ret;
        }
 }
 
@@ -181,8 +206,7 @@ _vte_file_stream_append (VteStream *astream, const char *data, gsize len)
 
        _vte_file_stream_ensure_fd0 (stream);
 
-       lseek (stream->fd[0], 0, SEEK_END);
-       _xwrite (stream->fd[0], data, len);
+       _xpwrite (stream->fd[0], data, len, stream->head);
        stream->head += len;
 }
 
@@ -196,13 +220,11 @@ _vte_file_stream_read (VteStream *astream, gsize offset, char *data, gsize len)
                return FALSE;
 
        if (offset < stream->offset[0]) {
-               lseek (stream->fd[1], offset - stream->offset[1], SEEK_SET);
-               l = _xread (stream->fd[1], data, len);
+               l = _xpread (stream->fd[1], data, len, offset - stream->offset[1]);
                offset += l; data += l; len -= l; if (!len) return TRUE;
        }
 
-       lseek (stream->fd[0], offset - stream->offset[0], SEEK_SET);
-       l = _xread (stream->fd[0], data, len);
+       l = _xpread (stream->fd[0], data, len, offset - stream->offset[0]);
        offset += l; data += l; len -= l; if (!len) return TRUE;
 
        return FALSE;