net/lapb/lapb_out.c


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/*
 *	LAPB release 002
 *
 *	This code REQUIRES 2.1.15 or higher/ NET3.038
 *
 *	This module:
 *		This module is free software; you can redistribute it and/or
 *		modify it under the terms of the GNU General Public License
 *		as published by the Free Software Foundation; either version
 *		2 of the License, or (at your option) any later version.
 *
 *	History
 *	LAPB 001	Jonathan Naylor	Started Coding
 *	LAPB 002	Jonathan Naylor	New timer architecture.
 */

#include <linux/errno.h>
#include <linux/types.h>
#include <linux/socket.h>
#include <linux/in.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/timer.h>
#include <linux/string.h>
#include <linux/sockios.h>
#include <linux/net.h>
#include <linux/inet.h>
#include <linux/skbuff.h>
#include <net/sock.h>
#include <asm/uaccess.h>
#include <asm/system.h>
#include <linux/fcntl.h>
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <net/lapb.h>

/* 
 *  This procedure is passed a buffer descriptor for an iframe. It builds
 *  the rest of the control part of the frame and then writes it out.
 */
static void lapb_send_iframe(struct lapb_cb *lapb, struct sk_buff *skb, int poll_bit)
{
	unsigned char *frame;

	if (!skb)
		return;

	if (lapb->mode & LAPB_EXTENDED) {
		frame = skb_push(skb, 2);

		frame[0] = LAPB_I;
		frame[0] |= lapb->vs << 1;
		frame[1] = poll_bit ? LAPB_EPF : 0;
		frame[1] |= lapb->vr << 1;
	} else {
		frame = skb_push(skb, 1);

		*frame = LAPB_I;
		*frame |= poll_bit ? LAPB_SPF : 0;
		*frame |= lapb->vr << 5;
		*frame |= lapb->vs << 1;
	}

#if LAPB_DEBUG > 1
	printk(KERN_DEBUG "lapb: (%p) S%d TX I(%d) S%d R%d\n",
	       lapb->dev, lapb->state, poll_bit, lapb->vs, lapb->vr);
#endif

	lapb_transmit_buffer(lapb, skb, LAPB_COMMAND);	
}

void lapb_kick(struct lapb_cb *lapb)
{
	struct sk_buff *skb, *skbn;
	unsigned short modulus, start, end;

	modulus = (lapb->mode & LAPB_EXTENDED) ? LAPB_EMODULUS : LAPB_SMODULUS;
	start = !skb_peek(&lapb->ack_queue) ? lapb->va : lapb->vs;
	end   = (lapb->va + lapb->window) % modulus;

	if (!(lapb->condition & LAPB_PEER_RX_BUSY_CONDITION) &&
	    start != end && skb_peek(&lapb->write_queue)) {
		lapb->vs = start;

		/*
		 * Dequeue the frame and copy it.
		 */
		skb = skb_dequeue(&lapb->write_queue);

		do {
			if ((skbn = skb_clone(skb, GFP_ATOMIC)) == NULL) {
				skb_queue_head(&lapb->write_queue, skb);
				break;
			}

			if (skb->sk)
				skb_set_owner_w(skbn, skb->sk);

			/*
			 * Transmit the frame copy.
			 */
			lapb_send_iframe(lapb, skbn, LAPB_POLLOFF);

			lapb->vs = (lapb->vs + 1) % modulus;

			/*
			 * Requeue the original data frame.
			 */
			skb_queue_tail(&lapb->ack_queue, skb);

		} while (lapb->vs != end && (skb = skb_dequeue(&lapb->write_queue)) != NULL);

		lapb->condition &= ~LAPB_ACK_PENDING_CONDITION;

		if (!lapb_t1timer_running(lapb))
			lapb_start_t1timer(lapb);
	}
}

void lapb_transmit_buffer(struct lapb_cb *lapb, struct sk_buff *skb, int type)
{
	unsigned char *ptr;

	ptr = skb_push(skb, 1);

	if (lapb->mode & LAPB_MLP) {
		if (lapb->mode & LAPB_DCE) {
			if (type == LAPB_COMMAND)
				*ptr = LAPB_ADDR_C;
			if (type == LAPB_RESPONSE)
				*ptr = LAPB_ADDR_D;
		} else {
			if (type == LAPB_COMMAND)
				*ptr = LAPB_ADDR_D;
			if (type == LAPB_RESPONSE)
				*ptr = LAPB_ADDR_C;
		}
	} else {
		if (lapb->mode & LAPB_DCE) {
			if (type == LAPB_COMMAND)
				*ptr = LAPB_ADDR_A;
			if (type == LAPB_RESPONSE)
				*ptr = LAPB_ADDR_B;
		} else {
			if (type == LAPB_COMMAND)
				*ptr = LAPB_ADDR_B;
			if (type == LAPB_RESPONSE)
				*ptr = LAPB_ADDR_A;
		}
	}

#if LAPB_DEBUG > 2
	printk(KERN_DEBUG "lapb: (%p) S%d TX %02X %02X %02X\n",
	       lapb->dev, lapb->state,
	       skb->data[0], skb->data[1], skb->data[2]);
#endif

	if (!lapb_data_transmit(lapb, skb))
		kfree_skb(skb);
}

void lapb_establish_data_link(struct lapb_cb *lapb)
{
	lapb->condition = 0x00;
	lapb->n2count   = 0;

	if (lapb->mode & LAPB_EXTENDED) {
#if LAPB_DEBUG > 1
		printk(KERN_DEBUG "lapb: (%p) S%d TX SABME(1)\n",
		       lapb->dev, lapb->state);
#endif
		lapb_send_control(lapb, LAPB_SABME, LAPB_POLLON, LAPB_COMMAND);
	} else {
#if LAPB_DEBUG > 1
		printk(KERN_DEBUG "lapb: (%p) S%d TX SABM(1)\n",
		       lapb->dev, lapb->state);
#endif
		lapb_send_control(lapb, LAPB_SABM, LAPB_POLLON, LAPB_COMMAND);
	}

	lapb_start_t1timer(lapb);
	lapb_stop_t2timer(lapb);
}

void lapb_enquiry_response(struct lapb_cb *lapb)
{
#if LAPB_DEBUG > 1
	printk(KERN_DEBUG "lapb: (%p) S%d TX RR(1) R%d\n",
	       lapb->dev, lapb->state, lapb->vr);
#endif

	lapb_send_control(lapb, LAPB_RR, LAPB_POLLON, LAPB_RESPONSE);

	lapb->condition &= ~LAPB_ACK_PENDING_CONDITION;
}

void lapb_timeout_response(struct lapb_cb *lapb)
{
#if LAPB_DEBUG > 1
	printk(KERN_DEBUG "lapb: (%p) S%d TX RR(0) R%d\n",
	       lapb->dev, lapb->state, lapb->vr);
#endif
	lapb_send_control(lapb, LAPB_RR, LAPB_POLLOFF, LAPB_RESPONSE);

	lapb->condition &= ~LAPB_ACK_PENDING_CONDITION;
}

void lapb_check_iframes_acked(struct lapb_cb *lapb, unsigned short nr)
{
	if (lapb->vs == nr) {
		lapb_frames_acked(lapb, nr);
		lapb_stop_t1timer(lapb);
		lapb->n2count = 0;
	} else if (lapb->va != nr) {
		lapb_frames_acked(lapb, nr);
		lapb_start_t1timer(lapb);
	}
}

void lapb_check_need_response(struct lapb_cb *lapb, int type, int pf)
{
	if (type == LAPB_COMMAND && pf)
		lapb_enquiry_response(lapb);
}
/**
 * attrib.c - NTFS attribute operations.  Part of the Linux-NTFS project.
 *
 * Copyright (c) 2001-2007 Anton Altaparmakov
 * Copyright (c) 2002 Richard Russon
 *
 * This program/include file is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as published
 * by the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program/include file is distributed in the hope that it will be
 * useful, but WITHOUT ANY WARRANTY; without even the implied warranty
 * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program (in the main directory of the Linux-NTFS
 * distribution in the file COPYING); if not, write to the Free Software
 * Foundation,Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include <linux/buffer_head.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/swap.h>
#include <linux/writeback.h>

#include "attrib.h"
#include "debug.h"
#include "layout.h"
#include "lcnalloc.h"
#include "malloc.h"
#include "mft.h"
#include "ntfs.h"
#include "types.h"

/**
 * ntfs_map_runlist_nolock - map (a part of) a runlist of an ntfs inode
 * @ni:		ntfs inode for which to map (part of) a runlist
 * @vcn:	map runlist part containing this vcn
 * @ctx:	active attribute search context if present or NULL if not
 *
 * Map the part of a runlist containing the @vcn of the ntfs inode @ni.
 *
 * If @ctx is specified, it is an active search context of @ni and its base mft
 * record.  This is needed when ntfs_map_runlist_nolock() encounters unmapped
 * runlist fragments and allows their mapping.  If you do not have the mft
 * record mapped, you can specify @ctx as NULL and ntfs_map_runlist_nolock()
 * will perform the necessary mapping and unmapping.
 *
 * Note, ntfs_map_runlist_nolock() saves the state of @ctx on entry and
 * restores it before returning.  Thus, @ctx will be left pointing to the same
 * attribute on return as on entry.  However, the actual pointers in @ctx may
 * point to different memory locations on return, so you must remember to reset
 * any cached pointers from the @ctx, i.e. after the call to
 * ntfs_map_runlist_nolock(), you will probably want to do:
 *	m = ctx->mrec;
 *	a = ctx->attr;
 * Assuming you cache ctx->attr in a variable @a of type ATTR_RECORD * and that
 * you cache ctx->mrec in a variable @m of type MFT_RECORD *.
 *
 * Return 0 on success and -errno on error.  There is one special error code
 * which is not an error as such.  This is -ENOENT.  It means that @vcn is out
 * of bounds of the runlist.
 *
 * Note the runlist can be NULL after this function returns if @vcn is zero and
 * the attribute has zero allocated size, i.e. there simply is no runlist.
 *
 * WARNING: If @ctx is supplied, regardless of whether success or failure is
 *	    returned, you need to check IS_ERR(@ctx->mrec) and if 'true' the @ctx
 *	    is no longer valid, i.e. you need to either call
 *	    ntfs_attr_reinit_search_ctx() or ntfs_attr_put_search_ctx() on it.
 *	    In that case PTR_ERR(@ctx->mrec) will give you the error code for
 *	    why the mapping of the old inode failed.
 *
 * Locking: - The runlist described by @ni must be locked for writing on entry
 *	      and is locked on return.  Note the runlist will be modified.
 *	    - If @ctx is NULL, the base mft record of @ni must not be mapped on
 *	      entry and it will be left unmapped on return.
 *	    - If @ctx is not NULL, the base mft record must be mapped on entry
 *	      and it will be left mapped on return.
 */
int ntfs_map_runlist_nolock(ntfs_inode *ni, VCN vcn, ntfs_attr_search_ctx *ctx)
{
	VCN end_vcn;
	unsigned long flags;
	ntfs_inode *base_ni;
	MFT_RECORD *m;
	ATTR_RECORD *a;
	runlist_element *rl;
	struct page *put_this_page = NULL;
	int err = 0;
	bool ctx_is_temporary, ctx_needs_reset;
	ntfs_attr_search_ctx old_ctx = { NULL, };

	ntfs_debug("Mapping runlist part containing vcn 0x%llx.",
			(unsigned long long)vcn);
	if (!NInoAttr(ni))
		base_ni = ni;
	else
		base_ni = ni->ext.base_ntfs_ino;
	if (!ctx) {
		ctx_is_temporary = ctx_needs_reset = true;
		m = map_mft_record(base_ni);
		if (IS_ERR(m))
			return PTR_ERR(m);
		ctx = ntfs_attr_get_search_ctx(base_ni, m);
		if (unlikely(!ctx)) {
			err = -ENOMEM;
			goto err_out;
		}
	} else {
		VCN allocated_size_vcn;

		BUG_ON(IS_ERR(ctx->mrec));
		a = ctx->attr;
		BUG_ON(!a->non_resident);
		ctx_is_temporary = false;
		end_vcn = sle64_to_cpu(a->data.non_resident.highest_vcn);
		read_lock_irqsave(&ni->size_lock, flags);
		allocated_size_vcn = ni->allocated_size >>
				ni->vol->cluster_size_bits;
		read_unlock_irqrestore(&ni->size_lock, flags);
		if (!a->data.non_resident.lowest_vcn && end_vcn <= 0)
			end_vcn = allocated_size_vcn - 1;
		/*
		 * If we already have the attribute extent containing @vcn in
		 * @ctx, no need to look it up again.  We slightly cheat in
		 * that if vcn exceeds the allocated size, we will refuse to
		 * map the runlist below, so there is definitely no need to get
		 * the right attribute extent.
		 */
		if (vcn >= allocated_size_vcn || (a->type == ni->type &&
				a->name_length == ni->name_len &&
				!memcmp((u8*)a + le16_to_cpu(a->name_offset),
				ni->name, ni->name_len) &&
				sle64_to_cpu(a->data.non_resident.lowest_vcn)
				<= vcn && end_vcn >= vcn))
			ctx_needs_reset = false;
		else {
			/* Save the old search context. */
			old_ctx = *ctx;
			/*
			 * If the currently mapped (extent) inode is not the
			 * base inode we will unmap it when we reinitialize the
			 * search context which means we need to get a
			 * reference to the page containing the mapped mft
			 * record so we do not accidentally drop changes to the
			 * mft record when it has not been marked dirty yet.
			 */
			if (old_ctx.base_ntfs_ino && old_ctx.ntfs_ino !=
					old_ctx.base_ntfs_ino) {
				put_this_page = old_ctx.ntfs_ino->page;
				page_cache_get(put_this_page);
			}
			/*
			 * Reinitialize the search context so we can lookup the
			 * needed attribute extent.
			 */
			ntfs_attr_reinit_search_ctx(ctx);
			ctx_needs_reset = true;
		}
	}
	if (ctx_needs_reset) {
		err = ntfs_attr_lookup(ni->type, ni->name, ni->name_len,
				CASE_SENSITIVE, vcn, NULL, 0, ctx);
		if (unlikely(err)) {
			if (err == -ENOENT)
				err = -EIO;
			goto err_out;
		}
		BUG_ON(!ctx->attr->non_resident);
	}
	a = ctx->attr;
	/*
	 * Only decompress the mapping pairs if @vcn is inside it.  Otherwise
	 * we get into problems when we try to map an out of bounds vcn because
	 * we then try to map the already mapped runlist fragment and
	 * ntfs_mapping_pairs_decompress() fails.
	 */
	end_vcn = sle64_to_cpu(a->data.non_resident.highest_vcn) + 1;
	if (unlikely(vcn && vcn >= end_vcn)) {
		err = -ENOENT;
		goto err_out;
	}
	rl = ntfs_mapping_pairs_decompress(ni->vol, a, ni->runlist.rl);
	if (IS_ERR(rl))
		err = PTR_ERR(rl);
	else
		ni->runlist.rl = rl;
err_out:
	if (ctx_is_temporary) {
		if (likely(ctx))
			ntfs_attr_put_search_ctx(ctx);
		unmap_mft_record(base_ni);
	} else if (ctx_needs_reset) {
		/*
		 * If there is no attribute list, restoring the search context
		 * is accomplished simply by copying the saved context back over
		 * the caller supplied context.  If there is an attribute list,
		 * things are more complicated as we need to deal with mapping
		 * of mft records and resulting potential changes in pointers.
		 */
		if (NInoAttrList(base_ni)) {
			/*
			 * If the currently mapped (extent) inode is not the
			 * one we had before, we need to unmap it and map the
			 * old one.
			 */
			if (ctx->ntfs_ino != old_ctx.ntfs_ino) {
				/*
				 * If the currently mapped inode is not the
				 * base inode, unmap it.
				 */
				if (ctx->base_ntfs_ino && ctx->ntfs_ino !=
						ctx->base_ntfs_ino) {
					unmap_extent_mft_record(ctx->ntfs_ino);
					ctx->mrec = ctx->base_mrec;
					BUG_ON(!ctx->mrec);
				}
				/*
				 * If the old mapped inode is not the base
				 * inode, map it.
				 */
				if (old_ctx.base_ntfs_ino &&
						old_ctx.ntfs_ino !=
						old_ctx.base_ntfs_ino) {
retry_map:
					ctx->mrec = map_mft_record(
							old_ctx.ntfs_ino);
					/*
					 * Something bad has happened.  If out
					 * of memory retry till it succeeds.
					 * Any other errors are fatal and we
					 * return the error code in ctx->mrec.
					 * Let the caller deal with it...  We
					 * just need to fudge things so the
					 * caller can reinit and/or put the
					 * search context safely.
					 */
					if (IS_ERR(ctx->mrec)) {
						if (PTR_ERR(ctx->mrec) ==
								-ENOMEM) {
							schedule();
							goto retry_map;
						} else
							old_ctx.ntfs_ino =
								old_ctx.
								base_ntfs_ino;
					}
				}
			}
			/* Update the changed pointers in the saved context. */
			if (ctx->mrec != old_ctx.mrec) {
				if (!IS_ERR(ctx->mrec))
					old_ctx.attr = (ATTR_RECORD*)(
							(u8*)ctx->mrec +
							((u8*)old_ctx.attr -
							(u8*)old_ctx.mrec));
				old_ctx.mrec = ctx->mrec;
			}
		}
		/* Restore the search context to the saved one. */
		*ctx = old_ctx;
		/*
		 * We drop the reference on the page we took earlier.  In the
		 * case that IS_ERR(ctx->mrec) is true this means we might lose
		 * some changes to the mft record that had been made between
		 * the last time it was marked dirty/written out and now.  This
		 * at this stage is not a problem as the mapping error is fatal
		 * enough that the mft record cannot be written out anyway and
		 * the caller is very likely to shutdown the whole inode
		 * immediately and mark the volume dirty for chkdsk to pick up
		 * the pieces anyway.
		 */
		if (put_this_page)
			page_cache_release(put_this_page);
	}
	return err;
}

/**
 * ntfs_map_runlist - map (a part of) a runlist of an ntfs inode
 * @ni:		ntfs inode for which to map (part of) a runlist
 * @vcn:	map runlist part containing this vcn
 *
 * Map the part of a runlist containing the @vcn of the ntfs inode @ni.
 *
 * Return 0 on success and -errno on error.  There is one special error code
 * which is not an error as such.  This is -ENOENT.  It means that @vcn is out
 * of bounds of the runlist.
 *
 * Locking: - The runlist must be unlocked on entry and is unlocked on return.
 *	    - This function takes the runlist lock for writing and may modify
 *	      the runlist.
 */
int ntfs_map_runlist(ntfs_inode *ni, VCN vcn)
{
	int err = 0;

	down_write(&ni->runlist.lock);
	/* Make sure someone else didn't do the work while we were sleeping. */
	if (likely(ntfs_rl_vcn_to_lcn(ni->runlist.rl, vcn) <=
			LCN_RL_NOT_MAPPED))
		err = ntfs_map_runlist_nolock(ni, vcn, NULL);
	up_write(&ni->runlist.lock);
	return err;
}

/**
 * ntfs_attr_vcn_to_lcn_nolock - convert a vcn into a lcn given an ntfs inode
 * @ni:			ntfs inode of the attribute whose runlist to search
 * @vcn:		vcn to convert
 * @write_locked:	true if the runlist is locked for writing
 *
 * Find the virtual cluster number @vcn in the runlist of the ntfs attribute
 * described by the ntfs inode @ni and return the corresponding logical cluster
 * number (lcn).
 *
 * If the @vcn is not mapped yet, the attempt is made to map the attribute
 * extent containing the @vcn and the vcn to lcn conversion is retried.
 *
 * If @write_locked is true the caller has locked the runlist for writing and
 * if false for reading.
 *
 * Since lcns must be >= 0, we use negative return codes with special meaning:
 *
 * Return code	Meaning / Description
 * ==========================================
 *  LCN_HOLE	Hole / not allocated on disk.
 *  LCN_ENOENT	There is no such vcn in the runlist, i.e. @vcn is out of bounds.
 *  LCN_ENOMEM	Not enough memory to map runlist.
 *  LCN_EIO	Critical error (runlist/file is corrupt, i/o error, etc).
 *
 * Locking: - The runlist must be locked on entry and is left locked on return.
 *	    - If @write_locked is 'false', i.e. the runlist is locked for reading,
 *	      the lock may be dropped inside the function so you cannot rely on
 *	      the runlist still being the same when this function returns.
 */
LCN ntfs_attr_vcn_to_lcn_nolock(ntfs_inode *ni, const VCN vcn,
		const bool write_locked)
{
	LCN lcn;
	unsigned long flags;
	bool is_retry = false;

	ntfs_debug("Entering for i_ino 0x%lx, vcn 0x%llx, %s_locked.",
			ni->mft_no, (unsigned long long)vcn,
			write_locked ? "write" : "read");
	BUG_ON(!ni);
	BUG_ON(!NInoNonResident(ni));
	BUG_ON(vcn < 0);
	if (!ni->runlist.rl) {
		read_lock_irqsave(&ni->size_lock, flags);
		if (!ni->allocated_size) {
			read_unlock_irqrestore(&ni->size_lock, flags);
			return LCN_ENOENT;
		}
		read_unlock_irqrestore(&ni->size_lock, flags);
	}
retry_remap:
	/* Convert vcn to lcn.  If that fails map the runlist and retry once. */
	lcn = ntfs_rl_vcn_to_lcn(ni->runlist.rl, vcn);
	if (likely(lcn >= LCN_HOLE)) {
		ntfs_debug("Done, lcn 0x%llx.", (long long)lcn);
		return lcn;
	}
	if (lcn != LCN_RL_NOT_MAPPED) {
		if (lcn != LCN_ENOENT)
			lcn = LCN_EIO;
	} else if (!is_retry) {
		int err;

		if (!write_locked) {
			up_read(&ni->runlist.lock);
			down_write(&ni->runlist.lock);
			if (unlikely(ntfs_rl_vcn_to_lcn(ni->runlist.rl, vcn) !=
					LCN_RL_NOT_MAPPED)) {
				up_write(&ni->runlist.lock);
				down_read(&ni->runlist.lock);
				goto retry_remap;
			}
		}
		err = ntfs_map_runlist_nolock(ni, vcn, NULL);
		if (!write_locked) {
			up_write(&ni->runlist.lock);
			down_read(&ni->runlist.lock);
		}
		if (likely(!err)) {
			is_retry = true;
			goto retry_remap;
		}
		if (err == -ENOENT)
			lcn = LCN_ENOENT;
		else if (err == -ENOMEM)
			lcn = LCN_ENOMEM;
		else
			lcn = LCN_EIO;
	}
	if (lcn != LCN_ENOENT)
		ntfs_error(ni->vol->sb, "Failed with error code %lli.",
				(long long)lcn);
	return lcn;
}

/**
 * ntfs_attr_find_vcn_nolock - find a vcn in the runlist of an ntfs inode
 * @ni:		ntfs inode describing the runlist to search
 * @vcn:	vcn to find
 * @ctx:	active attribute search context if present or NULL if not
 *
 * Find the virtual cluster number @vcn in the runlist described by the ntfs
 * inode @ni and return the address of the runlist element containing the @vcn.
 *
 * If the @vcn is not mapped yet, the attempt is made to map the attribute
 * extent containing the @vcn and the vcn to lcn conversion is retried.
 *
 * If @ctx is specified, it is an active search context of @ni and its base mft
 * record.  This is needed when ntfs_attr_find_vcn_nolock() encounters unmapped
 * runlist fragments and allows their mapping.  If you do not have the mft
 * record mapped, you can specify @ctx as NULL and ntfs_attr_find_vcn_nolock()
 * will perform the necessary mapping and unmapping.
 *
 * Note, ntfs_attr_find_vcn_nolock() saves the state of @ctx on entry and
 * restores it before returning.  Thus, @ctx will be left pointing to the same
 * attribute on return as on entry.  However, the actual pointers in @ctx may
 * point to different memory locations on return, so you must remember to reset
 * any cached pointers from the @ctx, i.e. after the call to
 * ntfs_attr_find_vcn_nolock(), you will probably want to do:
 *	m = ctx->mrec;
 *	a = ctx->attr;
 * Assuming you cache ctx->attr in a variable @a of type ATTR_RECORD * and that
 * you cache ctx->mrec in a variable @m of type MFT_RECORD *.
 * Note you need to distinguish between the lcn of the returned runlist element
 * being >= 0 and LCN_HOLE.  In the later case you have to return zeroes on
 * read and allocate clusters on write.
 *
 * Return the runlist element containing the @vcn on success and
 * ERR_PTR(-errno) on error.  You need to test the return value with IS_ERR()
 * to decide if the return is success or failure and PTR_ERR() to get to the
 * error code if IS_ERR() is true.
 *
 * The possible error return codes are:
 *	-ENOENT - No such vcn in the runlist, i.e. @vcn is out of bounds.
 *	-ENOMEM - Not enough memory to map runlist.
 *	-EIO	- Critical error (runlist/file is corrupt, i/o error, etc).
 *
 * WARNING: If @ctx is supplied, regardless of whether success or failure is
 *	    returned, you need to check IS_ERR(@ctx->mrec) and if 'true' the @ctx
 *	    is no longer valid, i.e. you need to either call
 *	    ntfs_attr_reinit_search_ctx() or ntfs_attr_put_search_ctx() on it.
 *	    In that case PTR_ERR(@ctx->mrec) will give you the error code for
 *	    why the mapping of the old inode failed.
 *
 * Locking: - The runlist described by @ni must be locked for writing on entry
 *	      and is locked on return.  Note the runlist may be modified when
 *	      needed runlist fragments need to be mapped.
 *	    - If @ctx is NULL, the base mft record of @ni must not be mapped on
 *	      entry and it will be left unmapped on return.
 *	    - If @ctx is not NULL, the base mft record must be mapped on entry
 *	      and it will be left mapped on return.
 */
runlist_element *ntfs_attr_find_vcn_nolock(ntfs_inode *ni, const VCN vcn,
		ntfs_attr_search_ctx *ctx)
{
	unsigned long flags;
	runlist_element *rl;
	int err = 0;
	bool is_retry = false;

	ntfs_debug("Entering for i_ino 0x%lx, vcn 0x%llx, with%s ctx.",
			ni->mft_no, (unsigned long long)vcn, ctx ? "" : "out");
	BUG_ON(!ni);
	BUG_ON(!NInoNonResident(ni));
	BUG_ON(vcn < 0);
	if (!ni->runlist.rl) {
		read_lock_irqsave(&ni->size_lock, flags);
		if (!ni->allocated_size) {
			read_unlock_irqrestore(&ni->size_lock, flags);
			return ERR_PTR(-ENOENT);
		}
		read_unlock_irqrestore(&ni->size_lock, flags);
	}
retry_remap:
	rl = ni->runlist.rl;
	if (likely(rl && vcn >= rl[0].vcn)) {
		while (likely(rl->length)) {
			if (unlikely(vcn < rl[1].vcn)) {
				if (likely(rl->lcn >= LCN_HOLE)) {
					ntfs_debug("Done.");
					return rl;
				}
				break;
			}
			rl++;
		}
		if (likely(rl->lcn != LCN_RL_NOT_MAPPED)) {
			if (likely(rl->lcn == LCN_ENOENT))
				err = -ENOENT;
			else
				err = -EIO;
		}
	}
	if (!err && !is_retry) {
		/*
		 * If the search context is invalid we cannot map the unmapped
		 * region.
		 */
		if (IS_ERR(ctx->mrec))
			err = PTR_ERR(ctx->mrec);
		else {
			/*
			 * The @vcn is in an unmapped region, map the runlist
			 * and retry.
			 */
			err = ntfs_map_runlist_nolock(ni, vcn, ctx);
			if (likely(!err)) {
				is_retry = true;
				goto retry_remap;
			}
		}
		if (err == -EINVAL)
			err = -EIO;
	} else if (!err)
		err = -EIO;
	if (err != -ENOENT)
		ntfs_error(ni->vol->sb, "Failed with error code %i.", err);
	return ERR_PTR(err);
}

/**
 * ntfs_attr_find - find (next) attribute in mft record
 * @type:	attribute type to find
 * @name:	attribute name to find (optional, i.e. NULL means don't care)
 * @name_len:	attribute name length (only needed if @name present)
 * @ic:		IGNORE_CASE or CASE_SENSITIVE (ignored if @name not present)
 * @val:	attribute value to find (optional, resident attributes only)
 * @val_len:	attribute value length
 * @ctx:	search context with mft record and attribute to search from
 *
 * You should not need to call this function directly.  Use ntfs_attr_lookup()
 * instead.
 *
 * ntfs_attr_find() takes a search context @ctx as parameter and searches the
 * mft record specified by @ctx->mrec, beginning at @ctx->attr, for an
 * attribute of @type, optionally @name and @val.
 *
 * If the attribute is found, ntfs_attr_find() returns 0 and @ctx->attr will
 * point to the found attribute.
 *
 * If the attribute is not found, ntfs_attr_find() returns -ENOENT and
 * @ctx->attr will point to the attribute before which the attribute being
 * searched for would need to be inserted if such an action were to be desired.
 *
 * On actual error, ntfs_attr_find() returns -EIO.  In this case @ctx->attr is
 * undefined and in particular do not rely on it not changing.
 *
 * If @ctx->is_first is 'true', the search begins with @ctx->attr itself.  If it
 * is 'false', the search begins after @ctx->attr.
 *
 * If @ic is IGNORE_CASE, the @name comparisson is not case sensitive and
 * @ctx->ntfs_ino must be set to the ntfs inode to which the mft record
 * @ctx->mrec belongs.  This is so we can get at the ntfs volume and hence at
 * the upcase table.  If @ic is CASE_SENSITIVE, the comparison is case
 * sensitive.  When @name is present, @name_len is the @name length in Unicode
 * characters.
 *
 * If @name is not present (NULL), we assume that the unnamed attribute is
 * being searched for.
 *
 * Finally, the resident attribute value @val is looked for, if present.  If
 * @val is not present (NULL), @val_len is ignored.
 *
 * ntfs_attr_find() only searches the specified mft record and it ignores the
 * presence of an attribute list attribute (unless it is the one being searched
 * for, obviously).  If you need to take attribute lists into consideration,
 * use ntfs_attr_lookup() instead (see below).  This also means that you cannot
 * use ntfs_attr_find() to search for extent records of non-resident
 * attributes, as extents with lowest_vcn != 0 are usually described by the
 * attribute list attribute only. - Note that it is possible that the first
 * extent is only in the attribute list while the last extent is in the base
 * mft record, so do not rely on being able to find the first extent in the
 * base mft record.
 *
 * Warning: Never use @val when looking for attribute types which can be
 *	    non-resident as this most likely will result in a crash!
 */
static int ntfs_attr_find(const ATTR_TYPE type, const ntfschar *name,
		const u32 name_len, const IGNORE_CASE_BOOL ic,
		const u8 *val, const u32 val_len, ntfs_attr_search_ctx *ctx)
{
	ATTR_RECORD *a;
	ntfs_volume *vol = ctx->ntfs_ino->vol;
	ntfschar *upcase = vol->upcase;
	u32 upcase_len = vol->upcase_len;

	/*
	 * Iterate over attributes in mft record starting at @ctx->attr, or the
	 * attribute following that, if @ctx->is_first is 'true'.
	 */
	if (ctx->is_first) {
		a = ctx->attr;
		ctx->is_first = false;
	} else
		a = (ATTR_RECORD*)((u8*)ctx->attr +
				le32_to_cpu(ctx->attr->length));
	for (;;	a = (ATTR_RECORD*)((u8*)a + le32_to_cpu(a->length))) {
		if ((u8*)a < (u8*)ctx->mrec || (u8*)a > (u8*)ctx->mrec +
				le32_to_cpu(ctx->mrec->bytes_allocated))
			break;
		ctx->attr = a;
		if (unlikely(le32_to_cpu(a->type) > le32_to_cpu(type) ||
				a->type == AT_END))
			return -ENOENT;
		if (unlikely(!a->length))
			break;
		if (a->type != type)
			continue;
		/*
		 * If @name is present, compare the two names.  If @name is
		 * missing, assume we want an unnamed attribute.
		 */
		if (!name) {
			/* The search failed if the found attribute is named. */
			if (a->name_length)
				return -ENOENT;
		} else if (!ntfs_are_names_equal(name, name_len,
			    (ntfschar*)((u8*)a + le16_to_cpu(a->name_offset)),
			    a->name_length, ic, upcase, upcase_len)) {
			register int rc;

			rc = ntfs_collate_names(name, name_len,
					(ntfschar*)((u8*)a +
					le16_to_cpu(a->name_offset)),
					a->name_length, 1, IGNORE_CASE,
					upcase, upcase_len);
			/*
			 * If @name collates before a->name, there is no
			 * matching attribute.
			 */
			if (rc == -1)
				return -ENOENT;
			/* If the strings are not equal, continue search. */
			if (rc)
				continue;
			rc = ntfs_collate_names(name, name_len,
					(ntfschar*)((u8*)a +
					le16_to_cpu(a->name_offset)),
					a->name_length, 1, CASE_SENSITIVE,
					upcase, upcase_len);
			if (rc == -1)
				return -ENOENT;
			if (rc)
				continue;
		}
		/*
		 * The names match or @name not present and attribute is
		 * unnamed.  If no @val specified, we have found the attribute
		 * and are done.
		 */
		if (!val)
			return 0;
		/* @val is present; compare values. */
		else {
			register int rc;

			rc = memcmp(val, (u8*)a + le16_to_cpu(
					a->data.resident.value_offset),
					min_t(u32, val_len, le32_to_cpu(
					a->data.resident.value_length)));
			/*
			 * If @val collates before the current attribute's
			 * value, there is no matching attribute.
			 */
			if (!rc) {
				register u32 avl;

				avl = le32_to_cpu(
						a->data.resident.value_length);
				if (val_len == avl)
					return 0;
				if (val_len < avl)
					return -ENOENT;
			} else if (rc < 0)
				return -ENOENT;
		}
	}
	ntfs_error(vol->sb, "Inode is corrupt.  Run chkdsk.");
	NVolSetErrors(vol);
	return -EIO;
}

/**
 * load_attribute_list - load an attribute list into memory
 * @vol:		ntfs volume from which to read
 * @runlist:		runlist of the attribute list
 * @al_start:		destination buffer
 * @size:		size of the destination buffer in bytes
 * @initialized_size:	initialized size of the attribute list
 *
 * Walk the runlist @runlist and load all clusters from it copying them into
 * the linear buffer @al. The maximum number of bytes copied to @al is @size
 * bytes. Note, @size does not need to be a multiple of the cluster size. If
 * @initialized_size is less than @size, the region in @al between
 * @initialized_size and @size will be zeroed and not read from disk.
 *
 * Return 0 on success or -errno on error.
 */
int load_attribute_list(ntfs_volume *vol, runlist *runlist, u8 *al_start,
		const s64 size, const s64 initialized_size)
{
	LCN lcn;
	u8 *al = al_start;
	u8 *al_end = al + initialized_size;
	runlist_element *rl;
	struct buffer_head *bh;
	struct super_block *sb;
	unsigned long block_size;
	unsigned long block, max_block;
	int err = 0;
	unsigned char block_size_bits;

	ntfs_debug("Entering.");
	if (!vol || !runlist || !al || size <= 0 || initialized_size < 0 ||
			initialized_size > size)
		return -EINVAL;
	if (!initialized_size) {
		memset(al, 0, size);
		return 0;
	}
	sb = vol->sb;
	block_size = sb->s_blocksize;
	block_size_bits = sb->s_blocksize_bits;
	down_read(&runlist->lock);
	rl = runlist->rl;
	if (!rl) {
		ntfs_error(sb, "Cannot read attribute list since runlist is "
				"missing.");
		goto err_out;	
	}
	/* Read all clusters specified by the runlist one run at a time. */
	while (rl->length) {
		lcn = ntfs_rl_vcn_to_lcn(rl, rl->vcn);
		ntfs_debug("Reading vcn = 0x%llx, lcn = 0x%llx.",
				(unsigned long long)rl->vcn,
				(unsigned long long)lcn);
		/* The attribute list cannot be sparse. */
		if (lcn < 0) {
			ntfs_error(sb, "ntfs_rl_vcn_to_lcn() failed.  Cannot "
					"read attribute list.");
			goto err_out;
		}
		block = lcn << vol->cluster_size_bits >> block_size_bits;
		/* Read the run from device in chunks of block_size bytes. */
		max_block = block + (rl->length << vol->cluster_size_bits >>
				block_size_bits);
		ntfs_debug("max_block = 0x%lx.", max_block);
		do {
			ntfs_debug("Reading block = 0x%lx.", block);
			bh = sb_bread(sb, block);
			if (!bh) {
				ntfs_error(sb, "sb_bread() failed. Cannot "
						"read attribute list.");
				goto err_out;
			}
			if (al + block_size >= al_end)
				goto do_final;
			memcpy(al, bh->b_data, block_size);
			brelse(bh);
			al += block_size;
		} while (++block < max_block);
		rl++;
	}
	if (initialized_size < size) {
initialize:
		memset(al_start + initialized_size, 0, size - initialized_size);
	}
done:
	up_read(&runlist->lock);
	return err;
do_final:
	if (al < al_end) {
		/*
		 * Partial block.
		 *
		 * Note: The attribute list can be smaller than its allocation
		 * by multiple clusters.  This has been encountered by at least
		 * two people running Windows XP, thus we cannot do any
		 * truncation sanity checking here. (AIA)
		 */
		memcpy(al, bh->b_data, al_end - al);
		brelse(bh);
		if (initialized_size < size)
			goto initialize;
		goto done;
	}
	brelse(bh);
	/* Real overflow! */
	ntfs_error(sb, "Attribute list buffer overflow. Read attribute list "
			"is truncated.");
err_out:
	err = -EIO;
	goto done;
}

/**
 * ntfs_external_attr_find - find an attribute in the attribute list of an inode
 * @type:	attribute type to find
 * @name:	attribute name to find (optional, i.e. NULL means don't care)
 * @name_len:	attribute name length (only needed if @name present)
 * @ic:		IGNORE_CASE or CASE_SENSITIVE (ignored if @name not present)
 * @lowest_vcn:	lowest vcn to find (optional, non-resident attributes only)
 * @val:	attribute value to find (optional, resident attributes only)
 * @val_len:	attribute value length
 * @ctx:	search context with mft record and attribute to search from
 *
 * You should not need to call this function directly.  Use ntfs_attr_lookup()
 * instead.
 *
 * Find an attribute by searching the attribute list for the corresponding
 * attribute list entry.  Having found the entry, map the mft record if the
 * attribute is in a different mft record/inode, ntfs_attr_find() the attribute
 * in there and return it.
 *
 * On first search @ctx->ntfs_ino must be the base mft record and @ctx must
 * have been obtained from a call to ntfs_attr_get_search_ctx().  On subsequent
 * calls @ctx->ntfs_ino can be any extent inode, too (@ctx->base_ntfs_ino is
 * then the base inode).
 *
 * After finishing with the attribute/mft record you need to call
 * ntfs_attr_put_search_ctx() to cleanup the search context (unmapping any
 * mapped inodes, etc).
 *
 * If the attribute is found, ntfs_external_attr_find() returns 0 and
 * @ctx->attr will point to the found attribute.  @ctx->mrec will point to the
 * mft record in which @ctx->attr is located and @ctx->al_entry will point to
 * the attribute list entry for the attribute.
 *
 * If the attribute is not found, ntfs_external_attr_find() returns -ENOENT and
 * @ctx->attr will point to the attribute in the base mft record before which
 * the attribute being searched for would need to be inserted if such an action
 * were to be desired.  @ctx->mrec will point to the mft record in which
 * @ctx->attr is located and @ctx->al_entry will point to the attribute list
 * entry of the attribute before which the attribute being searched for would
 * need to be inserted if such an action were to be desired.
 *
 * Thus to insert the not found attribute, one wants to add the attribute to
 * @ctx->mrec (the base mft record) and if there is not enough space, the
 * attribute should be placed in a newly allocated extent mft record.  The
 * attribute list entry for the inserted attribute should be inserted in the
 * attribute list attribute at @ctx->al_entry.
 *
 * On actual error, ntfs_external_attr_find() returns -EIO.  In this case
 * @ctx->attr is undefined and in particular do not rely on it not changing.
 */
static int ntfs_external_attr_find(const ATTR_TYPE type,
		const ntfschar *name, const u32 name_len,
		const IGNORE_CASE_BOOL ic, const VCN lowest_vcn,
		const u8 *val, const u32 val_len, ntfs_attr_search_ctx *ctx)
{
	ntfs_inode *base_ni, *ni;
	ntfs_volume *vol;
	ATTR_LIST_ENTRY *al_entry, *next_al_entry;
	u8 *al_start, *al_end;
	ATTR_RECORD *a;
	ntfschar *al_name;
	u32 al_name_len;
	int err = 0;
	static const char *es = " Unmount and run chkdsk.";

	ni = ctx->ntfs_ino;
	base_ni = ctx->base_ntfs_ino;
	ntfs_debug("Entering for inode 0x%lx, type 0x%x.", ni->mft_no, type);
	if (!base_ni) {
		/* First call happens with the base mft record. */
		base_ni = ctx->base_ntfs_ino = ctx->ntfs_ino;
		ctx->base_mrec = ctx->mrec;
	}
	if (ni == base_ni)
		ctx->base_attr = ctx->attr;
	if (type == AT_END)
		goto not_found;
	vol = base_ni->vol;
	al_start = base_ni->attr_list;
	al_end = al_start + base_ni->attr_list_size;
	if (!ctx->al_entry)
		ctx->al_entry = (ATTR_LIST_ENTRY*)al_start;
	/*
	 * Iterate over entries in attribute list starting at @ctx->al_entry,
	 * or the entry following that, if @ctx->is_first is 'true'.
	 */
	if (ctx->is_first) {
		al_entry = ctx->al_entry;
		ctx->is_first = false;
	} else
		al_entry = (ATTR_LIST_ENTRY*)((u8*)ctx->al_entry +
				le16_to_cpu(ctx->al_entry->length));
	for (;; al_entry = next_al_entry) {
		/* Out of bounds check. */
		if ((u8*)al_entry < base_ni->attr_list ||
				(u8*)al_entry > al_end)
			break;	/* Inode is corrupt. */
		ctx->al_entry = al_entry;
		/* Catch the end of the attribute list. */
		if ((u8*)al_entry == al_end)
			goto not_found;
		if (!al_entry->length)
			break;