/*-
 * 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"

/*
 * __wt_block_truncate --
 *	Truncate the file.
 */
int
__wt_block_truncate(WT_SESSION_IMPL *session, WT_BLOCK *block, wt_off_t len)
{
	WT_CONNECTION_IMPL *conn;
	WT_DECL_RET;

	conn = S2C(session);

	__wt_verbose(session,
	    WT_VERB_BLOCK, "truncate file to %" PRIuMAX, (uintmax_t)len);

	/*
	 * Truncate requires serialization, we depend on our caller for that.
	 *
	 * Truncation isn't a requirement of the block manager, it's only used
	 * to conserve disk space. Regardless of the underlying file system
	 * call's result, the in-memory understanding of the file size changes.
	 */
	block->size = block->extend_size = len;

	/*
	 * Backups are done by copying files outside of WiredTiger, potentially
	 * by system utilities. We cannot truncate the file during the backup
	 * window, we might surprise an application.
	 *
	 * This affects files that aren't involved in the backup (for example,
	 * doing incremental backups, which only copies log files, or targeted
	 * backups, stops all block truncation unnecessarily). We may want a
	 * more targeted solution at some point.
	 */
	if (!conn->hot_backup) {
		__wt_readlock(session, &conn->hot_backup_lock);
		if (!conn->hot_backup)
			ret = __wt_ftruncate(session, block->fh, len);
		__wt_readunlock(session, &conn->hot_backup_lock);
	}

	/*
	 * The truncate may fail temporarily or permanently (for example, there
	 * may be a file mapping if there's an open checkpoint on the file on a
	 * POSIX system, in which case the underlying function returns EBUSY).
	 * It's OK, we don't have to be able to truncate files.
	 */
	return (ret == EBUSY || ret == ENOTSUP ? 0 : ret);
}

/*
 * __wt_block_discard --
 *	Discard blocks from the system buffer cache.
 */
int
__wt_block_discard(WT_SESSION_IMPL *session, WT_BLOCK *block, size_t added_size)
{
	WT_DECL_RET;
	WT_FILE_HANDLE *handle;

	/* The file may not support this call. */
	handle = block->fh->handle;
	if (handle->fh_advise == NULL)
		return (0);

	/* The call may not be configured. */
	if (block->os_cache_max == 0)
		return (0);

	/*
	 * We're racing on the addition, but I'm not willing to serialize on it
	 * in the standard read path without evidence it's needed.
	 */
	if ((block->os_cache += added_size) <= block->os_cache_max)
		return (0);

	block->os_cache = 0;
	ret = handle->fh_advise(handle, (WT_SESSION *)session,
	    (wt_off_t)0, (wt_off_t)0, WT_FILE_HANDLE_DONTNEED);
	return (ret == EBUSY || ret == ENOTSUP ? 0 : ret);
}

/*
 * __wt_block_extend --
 *	Extend the file.
 */
static inline int
__wt_block_extend(WT_SESSION_IMPL *session, WT_BLOCK *block,
    WT_FH *fh, wt_off_t offset, size_t align_size, bool *release_lockp)
{
	WT_DECL_RET;
	WT_FILE_HANDLE *handle;

	/*
	 * The locking in this function is messy: by definition, the live system
	 * is locked when we're called, but that lock may have been acquired by
	 * our caller or our caller's caller. If our caller's lock, release_lock
	 * comes in set and this function can unlock it before returning (so it
	 * isn't held while extending the file). If it is our caller's caller,
	 * then release_lock comes in not set, indicating it cannot be released
	 * here.
	 *
	 * If we unlock here, we clear release_lock.
	 */

	/* If not configured to extend the file, we're done. */
	if (block->extend_len == 0)
		return (0);

	/*
	 * Extend the file in chunks.  We want to limit the number of threads
	 * extending the file at the same time, so choose the one thread that's
	 * crossing the extended boundary.  We don't extend newly created files,
	 * and it's theoretically possible we might wait so long our extension
	 * of the file is passed by another thread writing single blocks, that's
	 * why there's a check in case the extended file size becomes too small:
	 * if the file size catches up, every thread tries to extend it.
	 */
	if (block->extend_size > block->size &&
	    (offset > block->extend_size || offset +
	    block->extend_len + (wt_off_t)align_size < block->extend_size))
		return (0);

	/*
	 * File extension may require locking: some variants of the system call
	 * used to extend the file initialize the extended space. If a writing
	 * thread races with the extending thread, the extending thread might
	 * overwrite already written data, and that would be very, very bad.
	 */
	handle = fh->handle;
	if (handle->fh_extend == NULL && handle->fh_extend_nolock == NULL)
		return (0);

	/*
	 * Set the extend_size before releasing the lock, I don't want to read
	 * and manipulate multiple values without holding a lock.
	 *
	 * There's a race between the calculation and doing the extension, but
	 * it should err on the side of extend_size being smaller than the
	 * actual file size, and that's OK, we simply may do another extension
	 * sooner than otherwise.
	 */
	block->extend_size = block->size + block->extend_len * 2;

	/*
	 * Release any locally acquired lock if not needed to extend the file,
	 * extending the file may require updating on-disk file's metadata,
	 * which can be slow. (It may be a bad idea to configure for file
	 * extension on systems that require locking over the extend call.)
	 */
	if (handle->fh_extend_nolock != NULL && *release_lockp) {
		*release_lockp = false;
		__wt_spin_unlock(session, &block->live_lock);
	}

	/*
	 * The extend might fail (for example, the file is mapped into memory),
	 * or discover file extension isn't supported; both are OK.
	 */
	ret = __wt_fextend(session, fh, block->extend_size);
	return (ret == EBUSY || ret == ENOTSUP ? 0 : ret);
}

/*
 * __wt_block_write_size --
 *	Return the buffer size required to write a block.
 */
int
__wt_block_write_size(WT_SESSION_IMPL *session, WT_BLOCK *block, size_t *sizep)
{
	WT_UNUSED(session);

	/*
	 * We write the page size, in bytes, into the block's header as a 4B
	 * unsigned value, and it's possible for the engine to accept an item
	 * we can't write.  For example, a huge key/value where the allocation
	 * size has been set to something large will overflow 4B when it tries
	 * to align the write.  We could make this work (for example, writing
	 * the page size in units of allocation size or something else), but
	 * it's not worth the effort, writing 4GB objects into a btree makes
	 * no sense.  Limit the writes to (4GB - 1KB), it gives us potential
	 * mode bits, and I'm not interested in debugging corner cases anyway.
	 */
	*sizep = (size_t)
	    WT_ALIGN(*sizep + WT_BLOCK_HEADER_BYTE_SIZE, block->allocsize);
	return (*sizep > UINT32_MAX - 1024 ? EINVAL : 0);
}

/*
 * __wt_block_write --
 *	Write a buffer into a block, returning the block's address cookie.
 */
int
__wt_block_write(WT_SESSION_IMPL *session, WT_BLOCK *block, WT_ITEM *buf,
    uint8_t *addr, size_t *addr_sizep, bool data_checksum, bool checkpoint_io)
{
	wt_off_t offset;
	uint32_t checksum, size;
	uint8_t *endp;

	WT_RET(__wt_block_write_off(session, block, buf,
	    &offset, &size, &checksum, data_checksum, checkpoint_io, false));

	endp = addr;
	WT_RET(__wt_block_addr_to_buffer(block, &endp, offset, size, checksum));
	*addr_sizep = WT_PTRDIFF(endp, addr);

	return (0);
}

/*
 * __block_write_off --
 *	Write a buffer into a block, returning the block's offset, size and
 * checksum.
 */
static int
__block_write_off(WT_SESSION_IMPL *session, WT_BLOCK *block,
    WT_ITEM *buf, wt_off_t *offsetp, uint32_t *sizep, uint32_t *checksump,
    bool data_checksum, bool checkpoint_io, bool caller_locked)
{
	WT_BLOCK_HEADER *blk;
	WT_DECL_RET;
	WT_FH *fh;
	size_t align_size;
	wt_off_t offset;
	uint32_t checksum;
	bool local_locked;

	*offsetp = 0;			/* -Werror=maybe-uninitialized */
	*sizep = 0;			/* -Werror=maybe-uninitialized */
	*checksump = 0;			/* -Werror=maybe-uninitialized */

	fh = block->fh;

	/*
	 * Clear the block header to ensure all of it is initialized, even the
	 * unused fields.
	 */
	blk = WT_BLOCK_HEADER_REF(buf->mem);
	memset(blk, 0, sizeof(*blk));

	/* Buffers should be aligned for writing. */
	if (!F_ISSET(buf, WT_ITEM_ALIGNED)) {
		WT_ASSERT(session, F_ISSET(buf, WT_ITEM_ALIGNED));
		WT_RET_MSG(session, EINVAL,
		    "direct I/O check: write buffer incorrectly allocated");
	}

	/*
	 * Align the size to an allocation unit.
	 *
	 * The buffer must be big enough for us to zero to the next allocsize
	 * boundary, this is one of the reasons the btree layer must find out
	 * from the block-manager layer the maximum size of the eventual write.
	 */
	align_size = WT_ALIGN(buf->size, block->allocsize);
	if (align_size > buf->memsize) {
		WT_ASSERT(session, align_size <= buf->memsize);
		WT_RET_MSG(session, EINVAL,
		    "buffer size check: write buffer incorrectly allocated");
	}
	if (align_size > UINT32_MAX) {
		WT_ASSERT(session, align_size <= UINT32_MAX);
		WT_RET_MSG(session, EINVAL,
		    "buffer size check: write buffer too large to write");
	}

	/* Zero out any unused bytes at the end of the buffer. */
	memset((uint8_t *)buf->mem + buf->size, 0, align_size - buf->size);

	/*
	 * Set the disk size so we don't have to incrementally read blocks
	 * during salvage.
	 */
	blk->disk_size = WT_STORE_SIZE(align_size);

	/*
	 * Update the block's checksum: if our caller specifies, checksum the
	 * complete data, otherwise checksum the leading WT_BLOCK_COMPRESS_SKIP
	 * bytes.  The assumption is applications with good compression support
	 * turn off checksums and assume corrupted blocks won't decompress
	 * correctly.  However, if compression failed to shrink the block, the
	 * block wasn't compressed, in which case our caller will tell us to
	 * checksum the data to detect corruption. If compression succeeded,
	 * we still need to checksum the first WT_BLOCK_COMPRESS_SKIP bytes
	 * because they're not compressed, both to give salvage a quick test
	 * of whether a block is useful and to give us a test so we don't lose
	 * the first WT_BLOCK_COMPRESS_SKIP bytes without noticing.
	 *
	 * Checksum a little-endian version of the header, and write everything
	 * in little-endian format. The checksum is (potentially) returned in a
	 * big-endian format, swap it into place in a separate step.
	 */
	blk->flags = 0;
	if (data_checksum)
		F_SET(blk, WT_BLOCK_DATA_CKSUM);
	blk->checksum = 0;
	__wt_block_header_byteswap(blk);
	blk->checksum = checksum = __wt_checksum(
	    buf->mem, data_checksum ? align_size : WT_BLOCK_COMPRESS_SKIP);
#ifdef WORDS_BIGENDIAN
	blk->checksum = __wt_bswap32(blk->checksum);
#endif

	/* Pre-allocate some number of extension structures. */
	WT_RET(__wt_block_ext_prealloc(session, 5));

	/*
	 * Acquire a lock, if we don't already hold one.
	 * Allocate space for the write, and optionally extend the file (note
	 * the block-extend function may release the lock).
	 * Release any locally acquired lock.
	 */
	local_locked = false;
	if (!caller_locked) {
		__wt_spin_lock(session, &block->live_lock);
		local_locked = true;
	}
	ret = __wt_block_alloc(session, block, &offset, (wt_off_t)align_size);
	if (ret == 0)
		ret = __wt_block_extend(
		    session, block, fh, offset, align_size, &local_locked);
	if (local_locked)
		__wt_spin_unlock(session, &block->live_lock);
	WT_RET(ret);

	/* Write the block. */
	if ((ret =
	    __wt_write(session, fh, offset, align_size, buf->mem)) != 0) {
		if (!caller_locked)
			__wt_spin_lock(session, &block->live_lock);
		WT_TRET(__wt_block_off_free(
		    session, block, offset, (wt_off_t)align_size));
		if (!caller_locked)
			__wt_spin_unlock(session, &block->live_lock);
		WT_RET(ret);
	}

	/*
	 * Optionally schedule writes for dirty pages in the system buffer
	 * cache, but only if the current session can wait.
	 */
	if (block->os_cache_dirty_max != 0 &&
	    (block->os_cache_dirty += align_size) > block->os_cache_dirty_max &&
	    __wt_session_can_wait(session)) {
		block->os_cache_dirty = 0;
		if ((ret = __wt_fsync(session, fh, false)) != 0) {
			 /*
			  * Ignore ENOTSUP, but don't try again.
			  */
			if (ret != ENOTSUP)
				return (ret);
			block->os_cache_dirty_max = 0;
		}
	}

	/* Optionally discard blocks from the buffer cache. */
	WT_RET(__wt_block_discard(session, block, align_size));

	WT_STAT_CONN_INCR(session, block_write);
	WT_STAT_CONN_INCRV(session, block_byte_write, align_size);
	if (checkpoint_io)
		WT_STAT_CONN_INCRV(
		    session, block_byte_write_checkpoint, align_size);

	__wt_verbose(session, WT_VERB_WRITE,
	    "off %" PRIuMAX ", size %" PRIuMAX ", checksum %" PRIu32,
	    (uintmax_t)offset, (uintmax_t)align_size, checksum);

	*offsetp = offset;
	*sizep = WT_STORE_SIZE(align_size);
	*checksump = checksum;

	return (0);
}

/*
 * __wt_block_write_off --
 *	Write a buffer into a block, returning the block's offset, size and
 * checksum.
 */
int
__wt_block_write_off(WT_SESSION_IMPL *session, WT_BLOCK *block,
    WT_ITEM *buf, wt_off_t *offsetp, uint32_t *sizep, uint32_t *checksump,
    bool data_checksum, bool checkpoint_io, bool caller_locked)
{
	WT_DECL_RET;

	/*
	 * Ensure the page header is in little endian order; this doesn't belong
	 * here, but it's the best place to catch all callers. After the write,
	 * swap values back to native order so callers never see anything other
	 * than their original content.
	 */
	__wt_page_header_byteswap(buf->mem);
	ret = __block_write_off(session, block, buf, offsetp,
	    sizep, checksump, data_checksum, checkpoint_io, caller_locked);
	__wt_page_header_byteswap(buf->mem);
	return (ret);
}
