/*
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 * Functions for manipulating fifo buffers (that can grow if needed).
 *
 * As far as I am concerned, the code I have written for this software
 * can be used freely for any purpose.  Any derived versions of this
 * software must be clearly marked as such, and if the derived work is
 * incompatible with the protocol description in the RFC file, it must be
 * called by a name other than "ssh" or "Secure Shell".
 */

#include "includes.h"
RCSID("$OpenBSD: buffer.c,v 1.15 2002/01/18 18:14:17 stevesk Exp $");

#include "xmalloc.h"
#include "buffer.h"
#include "log.h"

/* Initializes the buffer structure. */

void
buffer_init(Buffer *buffer)
{
	buffer->alloc = 4096;
	buffer->buf = xmalloc(buffer->alloc);
	buffer->offset = 0;
	buffer->end = 0;
}

/* Frees any memory used for the buffer. */

void
buffer_free(Buffer *buffer)
{
	memset(buffer->buf, 0, buffer->alloc);
	xfree(buffer->buf);
}

/*
 * Clears any data from the buffer, making it empty.  This does not actually
 * zero the memory.
 */

void
buffer_clear(Buffer *buffer)
{
	buffer->offset = 0;
	buffer->end = 0;
}

/* Appends data to the buffer, expanding it if necessary. */

void
buffer_append(Buffer *buffer, const void *data, u_int len)
{
	void *p;
	p = buffer_append_space(buffer, len);
	memcpy(p, data, len);
}

/*
 * Appends space to the buffer, expanding the buffer if necessary. This does
 * not actually copy the data into the buffer, but instead returns a pointer
 * to the allocated region.
 */

void *
buffer_append_space(Buffer *buffer, u_int len)
{
	void *p;

	/* If the buffer is empty, start using it from the beginning. */
	if (buffer->offset == buffer->end) {
		buffer->offset = 0;
		buffer->end = 0;
	}
restart:
	/* If there is enough space to store all data, store it now. */
	if (buffer->end + len < buffer->alloc) {
		p = buffer->buf + buffer->end;
		buffer->end += len;
		return p;
	}
	/*
	 * If the buffer is quite empty, but all data is at the end, move the
	 * data to the beginning and retry.
	 */
	if (buffer->offset > buffer->alloc / 2) {
		memmove(buffer->buf, buffer->buf + buffer->offset,
			buffer->end - buffer->offset);
		buffer->end -= buffer->offset;
		buffer->offset = 0;
		goto restart;
	}
	/* Increase the size of the buffer and retry. */
	buffer->alloc += len + 32768;
	buffer->buf = xrealloc(buffer->buf, buffer->alloc);
	goto restart;
	/* NOTREACHED */
}

/* Returns the number of bytes of data in the buffer. */

u_int
buffer_len(Buffer *buffer)
{
	return buffer->end - buffer->offset;
}

/* Gets data from the beginning of the buffer. */

void
buffer_get(Buffer *buffer, void *buf, u_int len)
{
	if (len > buffer->end - buffer->offset)
		fatal("buffer_get: trying to get more bytes %d than in buffer %d",
		    len, buffer->end - buffer->offset);
	memcpy(buf, buffer->buf + buffer->offset, len);
	buffer->offset += len;
}

/* Consumes the given number of bytes from the beginning of the buffer. */

void
buffer_consume(Buffer *buffer, u_int bytes)
{
	if (bytes > buffer->end - buffer->offset)
		fatal("buffer_consume: trying to get more bytes than in buffer");
	buffer->offset += bytes;
}

/* Consumes the given number of bytes from the end of the buffer. */

void
buffer_consume_end(Buffer *buffer, u_int bytes)
{
	if (bytes > buffer->end - buffer->offset)
		fatal("buffer_consume_end: trying to get more bytes than in buffer");
	buffer->end -= bytes;
}

/* Returns a pointer to the first used byte in the buffer. */

void *
buffer_ptr(Buffer *buffer)
{
	return buffer->buf + buffer->offset;
}

/* Du
/*
 * linux/fs/jbd/commit.c
 *
 * Written by Stephen C. Tweedie <sct@redhat.com>, 1998
 *
 * Copyright 1998 Red Hat corp --- All Rights Reserved
 *
 * This file is part of the Linux kernel and is made available under
 * the terms of the GNU General Public License, version 2, or at your
 * option, any later version, incorporated herein by reference.
 *
 * Journal commit routines for the generic filesystem journaling code;
 * part of the ext2fs journaling system.
 */

#include <linux/time.h>
#include <linux/fs.h>
#include <linux/jbd.h>
#include <linux/errno.h>
#include <linux/slab.h>
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/bio.h>

/*
 * Default IO end handler for temporary BJ_IO buffer_heads.
 */
static void journal_end_buffer_io_sync(struct buffer_head *bh, int uptodate)
{
	BUFFER_TRACE(bh, "");
	if (uptodate)
		set_buffer_uptodate(bh);
	else
		clear_buffer_uptodate(bh);
	unlock_buffer(bh);
}

/*
 * When an ext3-ordered file is truncated, it is possible that many pages are
 * not successfully freed, because they are attached to a committing transaction.
 * After the transaction commits, these pages are left on the LRU, with no
 * ->mapping, and with attached buffers.  These pages are trivially reclaimable
 * by the VM, but their apparent absence upsets the VM accounting, and it makes
 * the numbers in /proc/meminfo look odd.
 *
 * So here, we have a buffer which has just come off the forget list.  Look to
 * see if we can strip all buffers from the backing page.
 *
 * Called under journal->j_list_lock.  The caller provided us with a ref
 * against the buffer, and we drop that here.
 */
static void release_buffer_page(struct buffer_head *bh)
{
	struct page *page;

	if (buffer_dirty(bh))
		goto nope;
	if (atomic_read(&bh->b_count) != 1)
		goto nope;
	page = bh->b_page;
	if (!page)
		goto nope;
	if (page->mapping)
		goto nope;

	/* OK, it's a truncated page */
	if (!trylock_page(page))
		goto nope;

	page_cache_get(page);
	__brelse(bh);
	try_to_free_buffers(page);
	unlock_page(page);
	page_cache_release(page);
	return;

nope:
	__brelse(bh);
}

/*
 * Decrement reference counter for data buffer. If it has been marked
 * 'BH_Freed', release it and the page to which it belongs if possible.
 */
static void release_data_buffer(struct buffer_head *bh)
{
	if (buffer_freed(bh)) {
		clear_buffer_freed(bh);
		release_buffer_page(bh);
	} else
		put_bh(bh);
}

/*
 * Try to acquire jbd_lock_bh_state() against the buffer, when j_list_lock is
 * held.  For ranking reasons we must trylock.  If we lose, schedule away and
 * return 0.  j_list_lock is dropped in this case.
 */
static int inverted_lock(journal_t *journal, struct buffer_head *bh)
{
	if (!jbd_trylock_bh_state(bh)) {
		spin_unlock(&journal->j_list_lock);
		schedule();
		return 0;
	}
	return 1;
}

/* Done it all: now write the commit record.  We should have
 * cleaned up our previous buffers by now, so if we are in abort
 * mode we can now just skip the rest of the journal write
 * entirely.
 *
 * Returns 1 if the journal needs to be aborted or 0 on success
 */
static int journal_write_commit_record(journal_t *journal,
					transaction_t *commit_transaction)
{
	struct journal_head *descriptor;
	struct buffer_head *bh;
	journal_header_t *header;
	int ret;
	int barrier_done = 0;

	if (is_journal_aborted(journal))
		return 0;

	descriptor = journal_get_descriptor_buffer(journal);
	if (!descriptor)
		return 1;

	bh = jh2bh(descriptor);

	header = (journal_header_t *)(bh->b_data);
	header->h_magic = cpu_to_be32(JFS_MAGIC_NUMBER);
	header->h_blocktype = cpu_to_be32(JFS_COMMIT_BLOCK);
	header->h_sequence = cpu_to_be32(commit_transaction->t_tid);

	JBUFFER_TRACE(descriptor, "write commit block");
	set_buffer_dirty(bh);
	if (journal->j_flags & JFS_BARRIER) {
		set_buffer_ordered(bh);
		barrier_done = 1;
	}
	ret = sync_dirty_buffer(bh);
	if (barrier_done)
		clear_buffer_ordered(bh);
	/* is it possible for another commit to fail at roughly
	 * the same time as this one?  If so, we don't want to
	 * trust the barrier flag in the super, but instead want
	 * to remember if we sent a barrier request
	 */
	if (ret == -EOPNOTSUPP && barrier_done) {
		char b[BDEVNAME_SIZE];

		printk(KERN_WARNING
			"JBD: barrier-based sync failed on %s - "
			"disabling barriers\n",
			bdevname(journal->j_dev, b));
		spin_lock(&journal->j_state_lock);
		journal->j_flags &= ~JFS_BARRIER;
		spin_unlock(&journal->j_state_lock);

		/* And try again, without the barrier */
		set_buffer_uptodate(bh);
		set_buffer_dirty(bh);
		ret = sync_dirty_buffer(bh);
	}
	put_bh(bh);		/* One for getblk() */
	journal_put_journal_head(descriptor);

	return (ret == -EIO);
}

static void journal_do_submit_data(struct buffer_head **wbuf, int bufs,
				   int write_op)
{
	int i;

	for (i = 0; i < bufs; i++) {
		wbuf[i]->b_end_io = end_buffer_write_sync;
		/* We use-up our safety reference in submit_bh() */
		submit_bh(write_op, wbuf[i]);
	}
}

/*
 *  Submit all the data buffers to disk
 */
static int journal_submit_data_buffers(journal_t *journal,
				       transaction_t *commit_transaction,
				       int write_op)
{
	struct journal_head *jh;
	struct buffer_head<