os_fallocate.c

/*-
 * Copyright (c) 2014-2016 MongoDB, Inc.
 * Copyright (c) 2008-2014 WiredTiger, Inc.
 *	All rights reserved.
 *
 * See the file LICENSE for redistribution information.
 */

#include "wt_internal.h"

#if defined(__linux__)
#include <linux/falloc.h>
#include <sys/syscall.h>
#endif

/*
 * __posix_std_fallocate --
 *	Linux fallocate call.
 */
static int
__posix_std_fallocate(
    WT_FILE_HANDLE *file_handle, WT_SESSION *wt_session,  wt_off_t offset)
{
	WT_UNUSED(wt_session);

#if defined(HAVE_FALLOCATE)
	WT_DECL_RET;
	WT_FILE_HANDLE_POSIX *pfh;

	pfh = (WT_FILE_HANDLE_POSIX *)file_handle;

	WT_SYSCALL_RETRY(fallocate(pfh->fd, 0, (wt_off_t)0, offset), ret);
	return (ret);
#else
	WT_UNUSED(file_handle);
	WT_UNUSED(offset);
	return (ENOTSUP);
#endif
}

/*
 * __posix_sys_fallocate --
 *	Linux fallocate call (system call version).
 */
static int
__posix_sys_fallocate(
    WT_FILE_HANDLE *file_handle, WT_SESSION *wt_session, wt_off_t offset)
{
	WT_UNUSED(wt_session);

#if defined(__linux__) && defined(SYS_fallocate)
	WT_DECL_RET;
	WT_FILE_HANDLE_POSIX *pfh;

	pfh = (WT_FILE_HANDLE_POSIX *)file_handle;

	/*
	 * Try the system call for fallocate even if the C library wrapper was
	 * not found.  The system call actually exists in the kernel for some
	 * Linux versions (RHEL 5.5), but not in the version of the C library.
	 * This allows it to work everywhere the kernel supports it.
	 */
	WT_SYSCALL_RETRY(
	    syscall(SYS_fallocate, pfh->fd, 0, (wt_off_t)0, offset), ret);
	return (ret);
#else
	WT_UNUSED(file_handle);
	WT_UNUSED(offset);
	return (ENOTSUP);
#endif
}

/*
 * __posix_posix_fallocate --
 *	POSIX fallocate call.
 */
static int
__posix_posix_fallocate(
    WT_FILE_HANDLE *file_handle, WT_SESSION *wt_session,  wt_off_t offset)
{
	WT_UNUSED(wt_session);

#if defined(HAVE_POSIX_FALLOCATE)
	WT_DECL_RET;
	WT_FILE_HANDLE_POSIX *pfh;

	pfh = (WT_FILE_HANDLE_POSIX *)file_handle;

	WT_SYSCALL_RETRY(posix_fallocate(pfh->fd, (wt_off_t)0, offset), ret);
	return (ret);
#else
	WT_UNUSED(file_handle);
	WT_UNUSED(offset);
	return (ENOTSUP);
#endif
}

/*
 * __wt_posix_file_extend --
 *	Extend the file.
 */
int
__wt_posix_file_extend(
    WT_FILE_HANDLE *file_handle, WT_SESSION *wt_session, wt_off_t offset)
{
	/*
	 * The first file extension call: figure out what this system has.
	 *
	 * This function is configured as a locking call, so we know we're
	 * single-threaded through here. Set the nolock function first, then
	 * publish the NULL replacement to ensure the handle functions are
	 * always correct.
	 *
	 * We've seen Linux systems where posix_fallocate has corrupted existing
	 * file data (even though that is explicitly disallowed by POSIX).
	 * FreeBSD and Solaris support posix_fallocate, and so far we've seen
	 * no problems leaving it unlocked. Check for fallocate (and the system
	 * call version of fallocate) first to avoid locking on Linux if at all
	 * possible.
	 */
	if (__posix_std_fallocate(file_handle, wt_session, offset) == 0) {
		file_handle->fh_extend_nolock = __posix_std_fallocate;
		WT_PUBLISH(file_handle->fh_extend, NULL);
		return (0);
	}
	if (__posix_sys_fallocate(file_handle, wt_session, offset) == 0) {
		file_handle->fh_extend_nolock = __posix_sys_fallocate;
		WT_PUBLISH(file_handle->fh_extend, NULL);
		return (0);
	}
	if (__posix_posix_fallocate(file_handle, wt_session, offset) == 0) {
#if defined(__linux__)
		file_handle->fh_extend = __posix_posix_fallocate;
		WT_WRITE_BARRIER();
#else
		file_handle->fh_extend_nolock = __posix_posix_fallocate;
		WT_PUBLISH(file_handle->fh_extend, NULL);
#endif
		return (0);
	}

	/*
	 * Use the POSIX ftruncate call if there's nothing else, it can extend
	 * files. Note ftruncate requires locking.
	 */
	if (file_handle->fh_truncate != NULL &&
	    file_handle->fh_truncate(file_handle, wt_session, offset) == 0) {
		file_handle->fh_extend = file_handle->fh_truncate;
		WT_WRITE_BARRIER();
		return (0);
	}

	file_handle->fh_extend = NULL;
	WT_WRITE_BARRIER();
	return (ENOTSUP);
}