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, 1 insertions, 0 deletions

diff --git a/erts/emulator/drivers/common/erl_efile.h b/erts/emulator/drivers/common/erl_efile.h
index 69ad02633c..b29b4f971c 100644
--- a/erts/emulator/drivers/common/erl_efile.h
+++ b/erts/emulator/drivers/common/erl_efile.h
@@ -185,3 +185,4 @@ int efile_fadvise(Efile_error* errInfo, int fd, Sint64 offset, Sint64 length,
 int efile_sendfile(Efile_error* errInfo, int in_fd, int out_fd,
 		      off_t *offset, Uint64 *nbytes, struct t_sendfile_hdtl *hdtl);
 #endif /* HAVE_SENDFILE */
+int efile_fallocate(Efile_error* errInfo, int fd, Sint64 offset, Sint64 length);