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[PATCH 1/2] pread: new module

From: Jim Meyering
Subject: [PATCH 1/2] pread: new module
Date: Wed, 25 Nov 2009 16:16:55 +0100 
We needed pread in libguestfs, so I wrote this:

>From f84e1a91fb3c43ba06567cbaeaf641135170d35a Mon Sep 17 00:00:00 2001
From: Jim Meyering <address@hidden>
Date: Wed, 25 Nov 2009 14:33:30 +0100
Subject: [PATCH 1/2] pread: new module

* modules/pread: New file.
* lib/pread.c (pread): New file.
* m4/pread.m4: Likewise.
* lib/unistd.in.h (pread): Define/declare.
* m4/unistd_h.m4 (gl_UNISTD_H_DEFAULTS): Define defaults.
* modules/unistd (Makefile.am): Substitute witnesses.
* doc/posix-functions/pread.texi (pread): Update.
* MODULES.html.sh: Add pread.
---
 ChangeLog                      |   11 +++++++
 MODULES.html.sh                |    1 +
 doc/posix-functions/pread.texi |    6 ++--
 lib/pread.c                    |   64 ++++++++++++++++++++++++++++++++++++++++
 lib/unistd.in.h                |   20 ++++++++++++
 m4/pread.m4                    |   15 +++++++++
 m4/unistd_h.m4                 |    3 ++
 modules/pread                  |   24 +++++++++++++++
 modules/unistd                 |    3 ++
 9 files changed, 144 insertions(+), 3 deletions(-)
 create mode 100644 lib/pread.c
 create mode 100644 m4/pread.m4
 create mode 100644 modules/pread

diff --git a/ChangeLog b/ChangeLog
index c0ce45b..c255af0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,16 @@
 2009-11-25  Jim Meyering  <address@hidden>

+       pread: new module
+       * modules/pread: New file.
+       * lib/unistd.in.h (pread): Define/declare.
+       * lib/pread.c (pread): New file.
+       * m4/unistd_h.m4 (gl_UNISTD_H_DEFAULTS): Define defaults.
+       * modules/unistd (Makefile.am): Substitute witnesses.
+       * doc/posix-functions/pread.texi (pread): Update.
+       * MODULES.html.sh: Add pread.
+
+2009-11-25  Jim Meyering  <address@hidden>
+
        tests/init.sh: new file to be used via most *.sh tests
        * tests/init.sh: New file.

diff --git a/MODULES.html.sh b/MODULES.html.sh
index 7fc55dd..9d5664a 100755
--- a/MODULES.html.sh
+++ b/MODULES.html.sh
@@ -1345,6 +1345,7 @@ h_errno
 index
 makecontext
 mktemp
+pread
 pthread_attr_getstackaddr
 pthread_attr_setstackaddr
 rindex
diff --git a/doc/posix-functions/pread.texi b/doc/posix-functions/pread.texi
index d1d6403..a11e36e 100644
--- a/doc/posix-functions/pread.texi
+++ b/doc/posix-functions/pread.texi
@@ -8,11 +8,11 @@ pread

 Portability problems fixed by Gnulib:
 @itemize
address@hidden
+This function is missing on some platforms:
+mingw, BeOS.
 @end itemize

 Portability problems not fixed by Gnulib:
 @itemize
address@hidden
-This function is missing on some platforms:
-mingw, BeOS.
 @end itemize
diff --git a/lib/pread.c b/lib/pread.c
new file mode 100644
index 0000000..632b914
--- /dev/null
+++ b/lib/pread.c
@@ -0,0 +1,64 @@
+/* replacement pread function
+   Copyright (C) 2009 Free Software Foundation, Inc.
+
+   This program 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 of the License, 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.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include <unistd.h>
+
+#include <errno.h>
+
+#define __libc_lseek(f,o,w) lseek (f, o, w)
+#define __set_errno(Val) errno = (Val)
+
+/* pread substitute for systems that the function, such as mingw32 and BeOS.  
*/
+/* The following is identical to the function from glibc's
+   sysdeps/posix/pread.c */
+
+/* Note: This implementation of pread is not multithread-safe.  */
+
+ssize_t
+pread (int fd, void *buf, size_t nbyte, off_t offset)
+{
+  /* Since we must not change the file pointer preserve the value so that
+     we can restore it later.  */
+  int save_errno;
+  ssize_t result;
+  off_t old_offset = __libc_lseek (fd, 0, SEEK_CUR);
+  if (old_offset == (off_t) -1)
+    return -1;
+
+  /* Set to wanted position.  */
+  if (__libc_lseek (fd, offset, SEEK_SET) == (off_t) -1)
+    return -1;
+
+  /* Write out the data.  */
+  result = __libc_read (fd, buf, nbyte);
+
+  /* Now we have to restore the position.  If this fails we have to
+     return this as an error.  But if the writing also failed we
+     return this error.  */
+  save_errno = errno;
+  if (__libc_lseek (fd, old_offset, SEEK_SET) == (off_t) -1)
+    {
+      if (result == -1)
+       __set_errno (save_errno);
+      return -1;
+    }
+  __set_errno (save_errno);
+
+  return result;
+}
diff --git a/lib/unistd.in.h b/lib/unistd.in.h
index 9a9a671..13d1bba 100644
--- a/lib/unistd.in.h
+++ b/lib/unistd.in.h
@@ -664,6 +664,26 @@ extern int pipe2 (int fd[2], int flags);
 #endif


+#if @GNULIB_PREAD@
+# if @REPLACE_PREAD@
+#  define pread rpl_pread
+# endif
+/* Read at most BUFSIZE bytes from FD into BUF, starting at OFFSET.
+   Return the number of bytes placed into BUF if successful, otherwise
+   set errno and return -1.  0 indicates EOF.  See the POSIX:2001
+   specification <http://www.opengroup.org/susv3xsh/pread.html>.  */
+# if address@hidden@ || @REPLACE_PREAD@
+  extern ssize_t pread (int fd, char *buf, size_t bufsize, off_t offset);
+# endif
+#elif defined GNULIB_POSIXCHECK
+# undef pread
+# define pread(f,b,s,o)                               \
+    (GL_LINK_WARNING ("pread is unportable - " \
+                      "use gnulib module pread for portability"), \
+     pread (f, b, s, o))
+#endif
+
+
 #if @GNULIB_READLINK@
 # if @REPLACE_READLINK@
 #  define readlink rpl_readlink
diff --git a/m4/pread.m4 b/m4/pread.m4
new file mode 100644
index 0000000..c281362
--- /dev/null
+++ b/m4/pread.m4
@@ -0,0 +1,15 @@
+# pread.m4 serial 1
+dnl Copyright (C) 2009 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+AC_DEFUN([gl_FUNC_PREAD],
+[
+  AC_REQUIRE([gl_UNISTD_H_DEFAULTS])
+  AC_CHECK_FUNCS_ONCE([pread])
+  if test $ac_cv_func_pread = no; then
+    HAVE_PREAD=0
+    AC_LIBOBJ([pread])
+  fi
+])
diff --git a/m4/unistd_h.m4 b/m4/unistd_h.m4
index 0a5b5d5..cb50d50 100644
--- a/m4/unistd_h.m4
+++ b/m4/unistd_h.m4
@@ -56,6 +56,7 @@ AC_DEFUN([gl_UNISTD_H_DEFAULTS],
   GNULIB_LINKAT=0;           AC_SUBST([GNULIB_LINKAT])
   GNULIB_LSEEK=0;            AC_SUBST([GNULIB_LSEEK])
   GNULIB_PIPE2=0;            AC_SUBST([GNULIB_PIPE2])
+  GNULIB_PREAD=0;            AC_SUBST([GNULIB_PREAD])
   GNULIB_READLINK=0;         AC_SUBST([GNULIB_READLINK])
   GNULIB_READLINKAT=0;       AC_SUBST([GNULIB_READLINKAT])
   GNULIB_RMDIR=0;            AC_SUBST([GNULIB_RMDIR])
@@ -87,6 +88,7 @@ AC_DEFUN([gl_UNISTD_H_DEFAULTS],
   HAVE_LINK=1;            AC_SUBST([HAVE_LINK])
   HAVE_LINKAT=1;          AC_SUBST([HAVE_LINKAT])
   HAVE_PIPE2=1;           AC_SUBST([HAVE_PIPE2])
+  HAVE_PREAD=1;           AC_SUBST([HAVE_PREAD])
   HAVE_READLINK=1;        AC_SUBST([HAVE_READLINK])
   HAVE_READLINKAT=1;      AC_SUBST([HAVE_READLINKAT])
   HAVE_SLEEP=1;           AC_SUBST([HAVE_SLEEP])
@@ -111,6 +113,7 @@ AC_DEFUN([gl_UNISTD_H_DEFAULTS],
   REPLACE_LINK=0;         AC_SUBST([REPLACE_LINK])
   REPLACE_LINKAT=0;       AC_SUBST([REPLACE_LINKAT])
   REPLACE_LSEEK=0;        AC_SUBST([REPLACE_LSEEK])
+  REPLACE_PREAD=0;        AC_SUBST([REPLACE_PREAD])
   REPLACE_READLINK=0;     AC_SUBST([REPLACE_READLINK])
   REPLACE_RMDIR=0;        AC_SUBST([REPLACE_RMDIR])
   REPLACE_SLEEP=0;        AC_SUBST([REPLACE_SLEEP])
diff --git a/modules/pread b/modules/pread
new file mode 100644
index 0000000..06039e6
--- /dev/null
+++ b/modules/pread
@@ -0,0 +1,24 @@
+Description:
+pread() function: read without changing file offset
+
+Files:
+lib/pread.c
+m4/pread.m4
+
+Depends-on:
+unistd
+
+configure.ac:
+gl_FUNC_PREAD
+gl_UNISTD_MODULE_INDICATOR([pread])
+
+Makefile.am:
+
+Include:
+<unistd.h>
+
+License:
+LGPLv2+
+
+Maintainer:
+Jim Meyering
diff --git a/modules/unistd b/modules/unistd
index 1282e53..7a55001 100644
--- a/modules/unistd
+++ b/modules/unistd
@@ -49,6 +49,7 @@ unistd.h: unistd.in.h
              -e 's|@''GNULIB_LINKAT''@|$(GNULIB_LINKAT)|g' \
              -e 's|@''GNULIB_LSEEK''@|$(GNULIB_LSEEK)|g' \
              -e 's|@''GNULIB_PIPE2''@|$(GNULIB_PIPE2)|g' \
+             -e 's|@''GNULIB_PREAD''@|$(GNULIB_PREAD)|g' \
              -e 's|@''GNULIB_READLINK''@|$(GNULIB_READLINK)|g' \
              -e 's|@''GNULIB_READLINKAT''@|$(GNULIB_READLINKAT)|g' \
              -e 's|@''GNULIB_RMDIR''@|$(GNULIB_RMDIR)|g' \
@@ -79,6 +80,7 @@ unistd.h: unistd.in.h
              -e 's|@''HAVE_LINK''@|$(HAVE_LINK)|g' \
              -e 's|@''HAVE_LINKAT''@|$(HAVE_LINKAT)|g' \
              -e 's|@''HAVE_PIPE2''@|$(HAVE_PIPE2)|g' \
+             -e 's|@''HAVE_PREAD''@|$(HAVE_PREAD)|g' \
              -e 's|@''HAVE_READLINK''@|$(HAVE_READLINK)|g' \
              -e 's|@''HAVE_READLINKAT''@|$(HAVE_READLINKAT)|g' \
              -e 's|@''HAVE_SLEEP''@|$(HAVE_SLEEP)|g' \
@@ -103,6 +105,7 @@ unistd.h: unistd.in.h
              -e 's|@''REPLACE_LINK''@|$(REPLACE_LINK)|g' \
              -e 's|@''REPLACE_LINKAT''@|$(REPLACE_LINKAT)|g' \
              -e 's|@''REPLACE_LSEEK''@|$(REPLACE_LSEEK)|g' \
+             -e 's|@''REPLACE_PREAD''@|$(REPLACE_PREAD)|g' \
              -e 's|@''REPLACE_READLINK''@|$(REPLACE_READLINK)|g' \
              -e 's|@''REPLACE_RMDIR''@|$(REPLACE_RMDIR)|g' \
              -e 's|@''REPLACE_SLEEP''@|$(REPLACE_SLEEP)|g' \
--
1.6.6.rc0.236.ge0b94
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