Add file:allocate/3 operation

This operation allows pre-allocation of space for files.
It succeeds only on systems that support such operation.

The POSIX standard defines the optional system call
posix_fallocate() to implement this feature. However,
some systems implement more specific functions to
accomplish the same operation.

On Linux, if the more specific function fallocate() is
implemented, it is used instead of posix_fallocate(),
falling back to posix_fallocate() if the fallocate()
call failed (it's only supported for the ext4, ocfs2,
xfs and btrfs file systems at the moment).

On Mac OS X it uses the specific fcntl() operation
F_PREALLOCATE, falling back to posix_fallocate() if
it's available (at the moment Mac OS X doesn't provide
posix_fallocate()).

On any other UNIX system, it uses posix_fallocate() if it's
available. Any other system not providing this system call
or any function to pre-allocate space for files, this operation
always fails with the ENOTSUP POSIX error.

1 files changed, 90 insertions, 2 deletions

diff --git a/erts/emulator/drivers/unix/unix_efile.c b/erts/emulator/drivers/unix/unix_efile.c
index cf7af71b92..558651fff9 100644
--- a/erts/emulator/drivers/unix/unix_efile.c
+++ b/erts/emulator/drivers/unix/unix_efile.c
@@ -22,6 +22,12 @@
 #ifdef HAVE_CONFIG_H
 #  include "config.h"
 #endif
+#if defined(HAVE_POSIX_FALLOCATE) && !defined(__sun) && !defined(__sun__)
+#define _XOPEN_SOURCE 600
+#endif
+#if !defined(_GNU_SOURCE) && defined(HAVE_LINUX_FALLOC_H)
+#define _GNU_SOURCE
+#endif
 #include "sys.h"
 #include "erl_driver.h"
 #include "erl_efile.h"
@@ -41,9 +47,13 @@
 #define DARWIN 1
 #endif
 
-#ifdef DARWIN
+#if defined(DARWIN) || defined(HAVE_LINUX_FALLOC_H) || defined(HAVE_POSIX_FALLOCATE)
 #include <fcntl.h>
-#endif /* DARWIN */
+#endif
+
+#ifdef HAVE_LINUX_FALLOC_H
+#include <linux/falloc.h>
+#endif
 
 #ifdef SUNOS4
 #  define getcwd(buf, size) getwd(buf)
@@ -967,3 +977,81 @@ efile_sendfile(Efile_error* errInfo, int in_fd, int out_fd,
     return check_error(retval, errInfo);
 }
 #endif /* HAVE_SENDFILE */
+
+#ifdef HAVE_POSIX_FALLOCATE
+static int
+call_posix_fallocate(int fd, Sint64 offset, Sint64 length)
+{
+    int ret;
+
+    /*
+     * On Linux and Solaris for example, posix_fallocate() returns
+     * a positive error number on error and it does not set errno.
+     * On FreeBSD however (9.0 at least), it returns -1 on error
+     * and it sets errno.
+     */
+    do {
+        ret = posix_fallocate(fd, (off_t) offset, (off_t) length);
+        if (ret > 0) {
+            errno = ret;
+            ret = -1;
+        }
+    } while (ret != 0 && errno == EINTR);
+
+    return ret;
+}
+#endif /* HAVE_POSIX_FALLOCATE */
+
+int
+efile_fallocate(Efile_error* errInfo, int fd, Sint64 offset, Sint64 length)
+{
+#if defined HAVE_FALLOCATE
+    /* Linux specific, more efficient than posix_fallocate. */
+    int ret;
+
+    do {
+        ret = fallocate(fd, FALLOC_FL_KEEP_SIZE, (off_t) offset, (off_t) length);
+    } while (ret != 0 && errno == EINTR);
+
+#if defined HAVE_POSIX_FALLOCATE
+    /* Fallback to posix_fallocate if available. */
+    if (ret != 0) {
+        ret = call_posix_fallocate(fd, offset, length);
+    }
+#endif
+
+    return check_error(ret, errInfo);
+#elif defined F_PREALLOCATE
+    /* Mac OS X specific, equivalent to posix_fallocate. */
+    int ret;
+    fstore_t fs;
+
+    memset(&fs, 0, sizeof(fs));
+    fs.fst_flags = F_ALLOCATECONTIG;
+    fs.fst_posmode = F_VOLPOSMODE;
+    fs.fst_offset = (off_t) offset;
+    fs.fst_length = (off_t) length;
+
+    ret = fcntl(fd, F_PREALLOCATE, &fs);
+
+    if (-1 == ret) {
+        fs.fst_flags = F_ALLOCATEALL;
+        ret = fcntl(fd, F_PREALLOCATE, &fs);
+
+#if defined HAVE_POSIX_FALLOCATE
+        /* Fallback to posix_fallocate if available. */
+        if (-1 == ret) {
+            ret = call_posix_fallocate(fd, offset, length);
+        }
+#endif
+    }
+
+    return check_error(ret, errInfo);
+#elif defined HAVE_POSIX_FALLOCATE
+    /* Other Unixes, use posix_fallocate if available. */
+    return check_error(call_posix_fallocate(fd, offset, length), errInfo);
+#else
+    errno = ENOTSUP;
+    return check_error(-1, errInfo);
+#endif
+}