Added pread and pwrite wrappers.

This adds wrappers for the pread and pwrite standard calls with fixed
semantics across all supported platforms.

The main variation (so far) is some platforms not having the calls at
all and AmigaOS not allowing seeks beyond existing extents.

2 files changed, 68 insertions, 1 deletions

diff --git a/src/Makefile b/src/Makefile
index 28bfc5f..b4fd96a 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -1,3 +1,3 @@
-DIR_SOURCES := base64.c time.c
+DIR_SOURCES := base64.c time.c unistd.c
 
 include $(NSBUILD)/Makefile.subdir
diff --git a/src/unistd.c b/src/unistd.c
new file mode 100644
index 0000000..219e9ec
--- /dev/null
+++ b/src/unistd.c
@@ -0,0 +1,67 @@
+/*
+ * Copyright 2015 Vincent Sanders <vince@netsurf-browser.org>
+ *
+ * This file is part of libnsutils.
+ *
+ * Licensed under the MIT License,
+ *                http://www.opensource.org/licenses/mit-license.php
+ */
+
+/**
+ * \file
+ * unistd style operations.
+ */
+
+#include <unistd.h>
+#include <errno.h>
+
+#include "nsutils/unistd.h"
+
+/* exported interface documented in nsutils/unistd.h */
+ssize_t nsu_pwrite(int fd, const void *buf, size_t count, off_t offset)
+{
+#if defined(__riscos) || defined(__amiga)
+        off_t sk;
+
+        sk = lseek(fd, offset, SEEK_SET);
+        if (sk == (off_t)-1) {
+#if defined(__amiga)
+                /* amigaos cannot seek past the end of the existing file so use
+                 * ftruncate to make the file long enough and retry the seek.
+                 */
+                int ret;
+                if (errno == ESPIPE) {
+                        ret = ftruncate(fd, offset);
+                        if (ret == -1) {
+                                return -1;
+                        }
+                        sk = lseek(fd, offset, SEEK_SET);
+                        if (sk == (off_t)-1) {
+                                return -1;
+                        }
+                } else
+#endif
+                return -1;
+        }
+        return write(fd, buf, count);
+#else
+        return pwrite(fd, buf, count, offset);
+#endif
+}
+
+/* exported interface documented in nsutils/unistd.h */
+ssize_t nsu_pread(int fd, void *buf, size_t count, off_t offset)
+{
+#if defined(__riscos)
+        off_t sk;
+
+        sk = lseek(fd, offset, SEEK_SET);
+        if (sk == -1) {
+                return (off_t)-1;
+        }
+        return read(fd, buf, count);
+#else
+        return pread(fd, buf, count, offset);
+#endif
+
+}