libctf: split up ctf-subr.c

This file is a bit of a grab-bag of dict-wide API functions like
ctf_set_open_errno or ctf_errwarning_next and portabilty functions and
wrappers like ctf_mmap or ctf_pread.

Split the latter out, and move other dict-wide functions that got
stuck in ctf-util.c (because it was so hard to tell the two files
apart) into ctf-api.c where they belong.

libctf/ctf-port.c

@@ -0,0 +1,122 @@
+/* Portability and helper wrappers.
+   Copyright (C) 2019-2024 Free Software Foundation, Inc.
+
+   This file is part of libctf.
+
+   libctf is free software; you can redistribute it and/or modify it under
+   the terms of the GNU General Public License as published by the Free
+   Software Foundation; either version 3, or (at your option) any later
+   version.
+
+   This program 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 General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; see the file COPYING.  If not see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <ctf-impl.h>
+#ifdef HAVE_MMAP
+#include <sys/mman.h>
+#endif
+#include <sys/types.h>
+#include <stdarg.h>
+#include <string.h>
+#include <unistd.h>
+
+/* Private, read-only mmap from a file, with fallback to copying.
+
+   No handling of page-offset issues at all: the caller must allow for that. */
+
+_libctf_malloc_ void *
+ctf_mmap (size_t length, size_t offset, int fd)
+{
+  void *data;
+
+#ifdef HAVE_MMAP
+  data = mmap (NULL, length, PROT_READ, MAP_PRIVATE, fd, offset);
+  if (data == MAP_FAILED)
+    data = NULL;
+#else
+  if ((data = malloc (length)) != NULL)
+    {
+      if (ctf_pread (fd, data, length, offset) <= 0)
+	{
+	  free (data);
+	  data = NULL;
+	}
+    }
+#endif
+  return data;
+}
+
+void
+ctf_munmap (void *buf, size_t length _libctf_unused_)
+{
+#ifdef HAVE_MMAP
+  (void) munmap (buf, length);
+#else
+  free (buf);
+#endif
+}
+
+/* pread() implementation, retrying on short reads.  */
+
+ssize_t
+ctf_pread (int fd, void *buf, ssize_t count, off_t offset)
+{
+  ssize_t len;
+  size_t acc = 0;
+  char *data = (char *) buf;
+
+#ifdef HAVE_PREAD
+  while (count > 0)
+    {
+      errno = 0;
+      if (((len = pread (fd, data, count, offset)) < 0) &&
+	  errno != EINTR)
+	  return len;
+      if (errno == EINTR)
+	continue;
+
+      acc += len;
+      if (len == 0)				/* EOF.  */
+	return acc;
+
+      count -= len;
+      offset += len;
+      data += len;
+    }
+  return acc;
+#else
+  off_t orig_off;
+
+  if ((orig_off = lseek (fd, 0, SEEK_CUR)) < 0)
+    return -1;
+  if ((lseek (fd, offset, SEEK_SET)) < 0)
+    return -1;
+
+  while (count > 0)
+    {
+      errno = 0;
+      if (((len = read (fd, data, count)) < 0) &&
+	  errno != EINTR)
+	  return len;
+      if (errno == EINTR)
+	continue;
+
+      acc += len;
+      if (len == 0)				/* EOF.  */
+	break;
+
+      count -= len;
+      data += len;
+    }
+  if ((lseek (fd, orig_off, SEEK_SET)) < 0)
+    return -1;					/* offset is smashed.  */
+#endif
+
+  return acc;
+}