fadvise: new module providing a simpler interface to posix_fadvise

* bootstrap.conf: Include the new module
* gl/lib/fadvise.c: Provide a simpler interface to posix_fadvise.
(fadvise): Provide hint to the whole file associated with a stream.
(fdadvise): Provide hint to the specific portion of a file
associated with a file descriptor.
* gl/lib/fadvise.h: Redefine POSIX_FADV_* to FADVISE_* enums.
* gl/modules/fadvise: New file.
* m4/jm-macros.m4: Remove the no longer needed posix_fadvise check.
* .x-sc_program_name: Exclude test-fadvise.c from this check.
* gl/tests/test-fadvise (main): New test program.
* gl/modules/fadvise-testss: A new index to reference the tests.
* src/sort.c (stream_open): Use the new interface.
* src/dd.c (iwrite): Likewise.

2 files changed, 109 insertions, 0 deletions

diff --git a/gl/lib/fadvise.c b/gl/lib/fadvise.c
new file mode 100644
index 000000000..cf2bc7028
--- /dev/null
+++ b/gl/lib/fadvise.c
@@ -0,0 +1,37 @@
+/* Declare an access pattern hint for files.
+   Copyright (C) 2010 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>
+#include "fadvise.h"
+
+#include <stdio.h>
+#include <fcntl.h>
+#include "ignore-value.h"
+
+void
+fdadvise (int fd, off_t offset, off_t len, fadvice_t advice)
+{
+#if HAVE_POSIX_FADVISE
+  ignore_value (posix_fadvise (fd, offset, len, advice));
+#endif
+}
+
+void
+fadvise (FILE *fp, fadvice_t advice)
+{
+  if (fp)
+    fdadvise (fileno (fp), 0, 0, advice);
+}
diff --git a/gl/lib/fadvise.h b/gl/lib/fadvise.h
new file mode 100644
index 000000000..fb84e75c9
--- /dev/null
+++ b/gl/lib/fadvise.h
@@ -0,0 +1,72 @@
+/* Declare an access pattern hint for files.
+   Copyright (C) 2010 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>
+#include <stdio.h>
+#include <fcntl.h>
+#include <sys/types.h>
+
+/* There are a few hints one can provide, which have the
+   following characteristics on Linux 2.6.31 at least.
+
+   POSIX_FADV_SEQUENTIAL
+     Doubles the size of read ahead done for file
+   POSIX_FADV_WILLNEED
+     _synchronously_ prepopulate the buffer cache with the file
+   POSIX_FADV_NOREUSE
+     Could lower priority of data in buffer caches,
+     but currently does nothing.
+   POSIX_FADV_DONTNEED
+     Drop the file from cache.
+     Note this is automatically done when files are unlinked.
+
+   We use this enum "type" both to make it explicit that
+   these options are mutually exclusive, and to discourage
+   the passing of the possibly undefined POSIX_FADV_... values.
+   Note we could #undef the POSIX_FADV_ values, but that would
+   preclude using the posix_fadvise() function with its standard
+   constants. Using posix_fadvise() might be required if the return
+   value is needed, but it must be guarded by appropriate #ifdefs.  */
+
+#if HAVE_POSIX_FADVISE
+typedef enum {
+  FADVISE_NORMAL =     POSIX_FADV_NORMAL,
+  FADVISE_SEQUENTIAL = POSIX_FADV_SEQUENTIAL,
+  FADVISE_NOREUSE =    POSIX_FADV_NOREUSE,
+  FADVISE_DONTNEED =   POSIX_FADV_DONTNEED,
+  FADVISE_WILLNEED =   POSIX_FADV_WILLNEED,
+  FADVISE_RANDOM =     POSIX_FADV_RANDOM,
+} fadvice_t;
+#else
+typedef enum {
+  FADVISE_NORMAL,
+  FADVISE_SEQUENTIAL,
+  FADVISE_NOREUSE,
+  FADVISE_DONTNEED,
+  FADVISE_WILLNEED,
+  FADVISE_RANDOM,
+} fadvice_t;
+#endif
+
+/* We ignore any errors as these hints are only advisory.
+   There is the chance one can pass invalid ADVICE, which will
+   not be indicated, but given the simplicity of the interface
+   this is unlikely.  Also not returning errors allows the
+   unconditional passing of descriptors to non standard files,
+   which will just be ignored if unsupported.  */
+
+void fdadvise (int fd, off_t offset, off_t len, fadvice_t advice);
+void fadvise (FILE *fp, fadvice_t advice);