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/fs/xfs/xfs_rtalloc.c

https://bitbucket.org/emiliolopez/linux
C | 1286 lines | 806 code | 50 blank | 430 comment | 183 complexity | f756e5369ca1e6da97359c77e2a7a9ef MD5 | raw file
   1/*
   2 * Copyright (c) 2000-2005 Silicon Graphics, Inc.
   3 * All Rights Reserved.
   4 *
   5 * This program is free software; you can redistribute it and/or
   6 * modify it under the terms of the GNU General Public License as
   7 * published by the Free Software Foundation.
   8 *
   9 * This program is distributed in the hope that it would be useful,
  10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12 * GNU General Public License for more details.
  13 *
  14 * You should have received a copy of the GNU General Public License
  15 * along with this program; if not, write the Free Software Foundation,
  16 * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  17 */
  18#include "xfs.h"
  19#include "xfs_fs.h"
  20#include "xfs_shared.h"
  21#include "xfs_format.h"
  22#include "xfs_log_format.h"
  23#include "xfs_trans_resv.h"
  24#include "xfs_bit.h"
  25#include "xfs_mount.h"
  26#include "xfs_defer.h"
  27#include "xfs_inode.h"
  28#include "xfs_bmap.h"
  29#include "xfs_bmap_util.h"
  30#include "xfs_bmap_btree.h"
  31#include "xfs_alloc.h"
  32#include "xfs_error.h"
  33#include "xfs_trans.h"
  34#include "xfs_trans_space.h"
  35#include "xfs_trace.h"
  36#include "xfs_buf.h"
  37#include "xfs_icache.h"
  38#include "xfs_rtalloc.h"
  39
  40
  41/*
  42 * Read and return the summary information for a given extent size,
  43 * bitmap block combination.
  44 * Keeps track of a current summary block, so we don't keep reading
  45 * it from the buffer cache.
  46 */
  47static int
  48xfs_rtget_summary(
  49	xfs_mount_t	*mp,		/* file system mount structure */
  50	xfs_trans_t	*tp,		/* transaction pointer */
  51	int		log,		/* log2 of extent size */
  52	xfs_rtblock_t	bbno,		/* bitmap block number */
  53	xfs_buf_t	**rbpp,		/* in/out: summary block buffer */
  54	xfs_fsblock_t	*rsb,		/* in/out: summary block number */
  55	xfs_suminfo_t	*sum)		/* out: summary info for this block */
  56{
  57	return xfs_rtmodify_summary_int(mp, tp, log, bbno, 0, rbpp, rsb, sum);
  58}
  59
  60/*
  61 * Return whether there are any free extents in the size range given
  62 * by low and high, for the bitmap block bbno.
  63 */
  64STATIC int				/* error */
  65xfs_rtany_summary(
  66	xfs_mount_t	*mp,		/* file system mount structure */
  67	xfs_trans_t	*tp,		/* transaction pointer */
  68	int		low,		/* low log2 extent size */
  69	int		high,		/* high log2 extent size */
  70	xfs_rtblock_t	bbno,		/* bitmap block number */
  71	xfs_buf_t	**rbpp,		/* in/out: summary block buffer */
  72	xfs_fsblock_t	*rsb,		/* in/out: summary block number */
  73	int		*stat)		/* out: any good extents here? */
  74{
  75	int		error;		/* error value */
  76	int		log;		/* loop counter, log2 of ext. size */
  77	xfs_suminfo_t	sum;		/* summary data */
  78
  79	/*
  80	 * Loop over logs of extent sizes.  Order is irrelevant.
  81	 */
  82	for (log = low; log <= high; log++) {
  83		/*
  84		 * Get one summary datum.
  85		 */
  86		error = xfs_rtget_summary(mp, tp, log, bbno, rbpp, rsb, &sum);
  87		if (error) {
  88			return error;
  89		}
  90		/*
  91		 * If there are any, return success.
  92		 */
  93		if (sum) {
  94			*stat = 1;
  95			return 0;
  96		}
  97	}
  98	/*
  99	 * Found nothing, return failure.
 100	 */
 101	*stat = 0;
 102	return 0;
 103}
 104
 105
 106/*
 107 * Copy and transform the summary file, given the old and new
 108 * parameters in the mount structures.
 109 */
 110STATIC int				/* error */
 111xfs_rtcopy_summary(
 112	xfs_mount_t	*omp,		/* old file system mount point */
 113	xfs_mount_t	*nmp,		/* new file system mount point */
 114	xfs_trans_t	*tp)		/* transaction pointer */
 115{
 116	xfs_rtblock_t	bbno;		/* bitmap block number */
 117	xfs_buf_t	*bp;		/* summary buffer */
 118	int		error;		/* error return value */
 119	int		log;		/* summary level number (log length) */
 120	xfs_suminfo_t	sum;		/* summary data */
 121	xfs_fsblock_t	sumbno;		/* summary block number */
 122
 123	bp = NULL;
 124	for (log = omp->m_rsumlevels - 1; log >= 0; log--) {
 125		for (bbno = omp->m_sb.sb_rbmblocks - 1;
 126		     (xfs_srtblock_t)bbno >= 0;
 127		     bbno--) {
 128			error = xfs_rtget_summary(omp, tp, log, bbno, &bp,
 129				&sumbno, &sum);
 130			if (error)
 131				return error;
 132			if (sum == 0)
 133				continue;
 134			error = xfs_rtmodify_summary(omp, tp, log, bbno, -sum,
 135				&bp, &sumbno);
 136			if (error)
 137				return error;
 138			error = xfs_rtmodify_summary(nmp, tp, log, bbno, sum,
 139				&bp, &sumbno);
 140			if (error)
 141				return error;
 142			ASSERT(sum > 0);
 143		}
 144	}
 145	return 0;
 146}
 147/*
 148 * Mark an extent specified by start and len allocated.
 149 * Updates all the summary information as well as the bitmap.
 150 */
 151STATIC int				/* error */
 152xfs_rtallocate_range(
 153	xfs_mount_t	*mp,		/* file system mount point */
 154	xfs_trans_t	*tp,		/* transaction pointer */
 155	xfs_rtblock_t	start,		/* start block to allocate */
 156	xfs_extlen_t	len,		/* length to allocate */
 157	xfs_buf_t	**rbpp,		/* in/out: summary block buffer */
 158	xfs_fsblock_t	*rsb)		/* in/out: summary block number */
 159{
 160	xfs_rtblock_t	end;		/* end of the allocated extent */
 161	int		error;		/* error value */
 162	xfs_rtblock_t	postblock = 0;	/* first block allocated > end */
 163	xfs_rtblock_t	preblock = 0;	/* first block allocated < start */
 164
 165	end = start + len - 1;
 166	/*
 167	 * Assume we're allocating out of the middle of a free extent.
 168	 * We need to find the beginning and end of the extent so we can
 169	 * properly update the summary.
 170	 */
 171	error = xfs_rtfind_back(mp, tp, start, 0, &preblock);
 172	if (error) {
 173		return error;
 174	}
 175	/*
 176	 * Find the next allocated block (end of free extent).
 177	 */
 178	error = xfs_rtfind_forw(mp, tp, end, mp->m_sb.sb_rextents - 1,
 179		&postblock);
 180	if (error) {
 181		return error;
 182	}
 183	/*
 184	 * Decrement the summary information corresponding to the entire
 185	 * (old) free extent.
 186	 */
 187	error = xfs_rtmodify_summary(mp, tp,
 188		XFS_RTBLOCKLOG(postblock + 1 - preblock),
 189		XFS_BITTOBLOCK(mp, preblock), -1, rbpp, rsb);
 190	if (error) {
 191		return error;
 192	}
 193	/*
 194	 * If there are blocks not being allocated at the front of the
 195	 * old extent, add summary data for them to be free.
 196	 */
 197	if (preblock < start) {
 198		error = xfs_rtmodify_summary(mp, tp,
 199			XFS_RTBLOCKLOG(start - preblock),
 200			XFS_BITTOBLOCK(mp, preblock), 1, rbpp, rsb);
 201		if (error) {
 202			return error;
 203		}
 204	}
 205	/*
 206	 * If there are blocks not being allocated at the end of the
 207	 * old extent, add summary data for them to be free.
 208	 */
 209	if (postblock > end) {
 210		error = xfs_rtmodify_summary(mp, tp,
 211			XFS_RTBLOCKLOG(postblock - end),
 212			XFS_BITTOBLOCK(mp, end + 1), 1, rbpp, rsb);
 213		if (error) {
 214			return error;
 215		}
 216	}
 217	/*
 218	 * Modify the bitmap to mark this extent allocated.
 219	 */
 220	error = xfs_rtmodify_range(mp, tp, start, len, 0);
 221	return error;
 222}
 223
 224/*
 225 * Attempt to allocate an extent minlen<=len<=maxlen starting from
 226 * bitmap block bbno.  If we don't get maxlen then use prod to trim
 227 * the length, if given.  Returns error; returns starting block in *rtblock.
 228 * The lengths are all in rtextents.
 229 */
 230STATIC int				/* error */
 231xfs_rtallocate_extent_block(
 232	xfs_mount_t	*mp,		/* file system mount point */
 233	xfs_trans_t	*tp,		/* transaction pointer */
 234	xfs_rtblock_t	bbno,		/* bitmap block number */
 235	xfs_extlen_t	minlen,		/* minimum length to allocate */
 236	xfs_extlen_t	maxlen,		/* maximum length to allocate */
 237	xfs_extlen_t	*len,		/* out: actual length allocated */
 238	xfs_rtblock_t	*nextp,		/* out: next block to try */
 239	xfs_buf_t	**rbpp,		/* in/out: summary block buffer */
 240	xfs_fsblock_t	*rsb,		/* in/out: summary block number */
 241	xfs_extlen_t	prod,		/* extent product factor */
 242	xfs_rtblock_t	*rtblock)	/* out: start block allocated */
 243{
 244	xfs_rtblock_t	besti;		/* best rtblock found so far */
 245	xfs_rtblock_t	bestlen;	/* best length found so far */
 246	xfs_rtblock_t	end;		/* last rtblock in chunk */
 247	int		error;		/* error value */
 248	xfs_rtblock_t	i;		/* current rtblock trying */
 249	xfs_rtblock_t	next;		/* next rtblock to try */
 250	int		stat;		/* status from internal calls */
 251
 252	/*
 253	 * Loop over all the extents starting in this bitmap block,
 254	 * looking for one that's long enough.
 255	 */
 256	for (i = XFS_BLOCKTOBIT(mp, bbno), besti = -1, bestlen = 0,
 257		end = XFS_BLOCKTOBIT(mp, bbno + 1) - 1;
 258	     i <= end;
 259	     i++) {
 260		/*
 261		 * See if there's a free extent of maxlen starting at i.
 262		 * If it's not so then next will contain the first non-free.
 263		 */
 264		error = xfs_rtcheck_range(mp, tp, i, maxlen, 1, &next, &stat);
 265		if (error) {
 266			return error;
 267		}
 268		if (stat) {
 269			/*
 270			 * i for maxlen is all free, allocate and return that.
 271			 */
 272			error = xfs_rtallocate_range(mp, tp, i, maxlen, rbpp,
 273				rsb);
 274			if (error) {
 275				return error;
 276			}
 277			*len = maxlen;
 278			*rtblock = i;
 279			return 0;
 280		}
 281		/*
 282		 * In the case where we have a variable-sized allocation
 283		 * request, figure out how big this free piece is,
 284		 * and if it's big enough for the minimum, and the best
 285		 * so far, remember it.
 286		 */
 287		if (minlen < maxlen) {
 288			xfs_rtblock_t	thislen;	/* this extent size */
 289
 290			thislen = next - i;
 291			if (thislen >= minlen && thislen > bestlen) {
 292				besti = i;
 293				bestlen = thislen;
 294			}
 295		}
 296		/*
 297		 * If not done yet, find the start of the next free space.
 298		 */
 299		if (next < end) {
 300			error = xfs_rtfind_forw(mp, tp, next, end, &i);
 301			if (error) {
 302				return error;
 303			}
 304		} else
 305			break;
 306	}
 307	/*
 308	 * Searched the whole thing & didn't find a maxlen free extent.
 309	 */
 310	if (minlen < maxlen && besti != -1) {
 311		xfs_extlen_t	p;	/* amount to trim length by */
 312
 313		/*
 314		 * If size should be a multiple of prod, make that so.
 315		 */
 316		if (prod > 1 && (p = do_mod(bestlen, prod)))
 317			bestlen -= p;
 318		/*
 319		 * Allocate besti for bestlen & return that.
 320		 */
 321		error = xfs_rtallocate_range(mp, tp, besti, bestlen, rbpp, rsb);
 322		if (error) {
 323			return error;
 324		}
 325		*len = bestlen;
 326		*rtblock = besti;
 327		return 0;
 328	}
 329	/*
 330	 * Allocation failed.  Set *nextp to the next block to try.
 331	 */
 332	*nextp = next;
 333	*rtblock = NULLRTBLOCK;
 334	return 0;
 335}
 336
 337/*
 338 * Allocate an extent of length minlen<=len<=maxlen, starting at block
 339 * bno.  If we don't get maxlen then use prod to trim the length, if given.
 340 * Returns error; returns starting block in *rtblock.
 341 * The lengths are all in rtextents.
 342 */
 343STATIC int				/* error */
 344xfs_rtallocate_extent_exact(
 345	xfs_mount_t	*mp,		/* file system mount point */
 346	xfs_trans_t	*tp,		/* transaction pointer */
 347	xfs_rtblock_t	bno,		/* starting block number to allocate */
 348	xfs_extlen_t	minlen,		/* minimum length to allocate */
 349	xfs_extlen_t	maxlen,		/* maximum length to allocate */
 350	xfs_extlen_t	*len,		/* out: actual length allocated */
 351	xfs_buf_t	**rbpp,		/* in/out: summary block buffer */
 352	xfs_fsblock_t	*rsb,		/* in/out: summary block number */
 353	xfs_extlen_t	prod,		/* extent product factor */
 354	xfs_rtblock_t	*rtblock)	/* out: start block allocated */
 355{
 356	int		error;		/* error value */
 357	xfs_extlen_t	i;		/* extent length trimmed due to prod */
 358	int		isfree;		/* extent is free */
 359	xfs_rtblock_t	next;		/* next block to try (dummy) */
 360
 361	ASSERT(minlen % prod == 0 && maxlen % prod == 0);
 362	/*
 363	 * Check if the range in question (for maxlen) is free.
 364	 */
 365	error = xfs_rtcheck_range(mp, tp, bno, maxlen, 1, &next, &isfree);
 366	if (error) {
 367		return error;
 368	}
 369	if (isfree) {
 370		/*
 371		 * If it is, allocate it and return success.
 372		 */
 373		error = xfs_rtallocate_range(mp, tp, bno, maxlen, rbpp, rsb);
 374		if (error) {
 375			return error;
 376		}
 377		*len = maxlen;
 378		*rtblock = bno;
 379		return 0;
 380	}
 381	/*
 382	 * If not, allocate what there is, if it's at least minlen.
 383	 */
 384	maxlen = next - bno;
 385	if (maxlen < minlen) {
 386		/*
 387		 * Failed, return failure status.
 388		 */
 389		*rtblock = NULLRTBLOCK;
 390		return 0;
 391	}
 392	/*
 393	 * Trim off tail of extent, if prod is specified.
 394	 */
 395	if (prod > 1 && (i = maxlen % prod)) {
 396		maxlen -= i;
 397		if (maxlen < minlen) {
 398			/*
 399			 * Now we can't do it, return failure status.
 400			 */
 401			*rtblock = NULLRTBLOCK;
 402			return 0;
 403		}
 404	}
 405	/*
 406	 * Allocate what we can and return it.
 407	 */
 408	error = xfs_rtallocate_range(mp, tp, bno, maxlen, rbpp, rsb);
 409	if (error) {
 410		return error;
 411	}
 412	*len = maxlen;
 413	*rtblock = bno;
 414	return 0;
 415}
 416
 417/*
 418 * Allocate an extent of length minlen<=len<=maxlen, starting as near
 419 * to bno as possible.  If we don't get maxlen then use prod to trim
 420 * the length, if given.  The lengths are all in rtextents.
 421 */
 422STATIC int				/* error */
 423xfs_rtallocate_extent_near(
 424	xfs_mount_t	*mp,		/* file system mount point */
 425	xfs_trans_t	*tp,		/* transaction pointer */
 426	xfs_rtblock_t	bno,		/* starting block number to allocate */
 427	xfs_extlen_t	minlen,		/* minimum length to allocate */
 428	xfs_extlen_t	maxlen,		/* maximum length to allocate */
 429	xfs_extlen_t	*len,		/* out: actual length allocated */
 430	xfs_buf_t	**rbpp,		/* in/out: summary block buffer */
 431	xfs_fsblock_t	*rsb,		/* in/out: summary block number */
 432	xfs_extlen_t	prod,		/* extent product factor */
 433	xfs_rtblock_t	*rtblock)	/* out: start block allocated */
 434{
 435	int		any;		/* any useful extents from summary */
 436	xfs_rtblock_t	bbno;		/* bitmap block number */
 437	int		error;		/* error value */
 438	int		i;		/* bitmap block offset (loop control) */
 439	int		j;		/* secondary loop control */
 440	int		log2len;	/* log2 of minlen */
 441	xfs_rtblock_t	n;		/* next block to try */
 442	xfs_rtblock_t	r;		/* result block */
 443
 444	ASSERT(minlen % prod == 0 && maxlen % prod == 0);
 445	/*
 446	 * If the block number given is off the end, silently set it to
 447	 * the last block.
 448	 */
 449	if (bno >= mp->m_sb.sb_rextents)
 450		bno = mp->m_sb.sb_rextents - 1;
 451	/*
 452	 * Try the exact allocation first.
 453	 */
 454	error = xfs_rtallocate_extent_exact(mp, tp, bno, minlen, maxlen, len,
 455		rbpp, rsb, prod, &r);
 456	if (error) {
 457		return error;
 458	}
 459	/*
 460	 * If the exact allocation worked, return that.
 461	 */
 462	if (r != NULLRTBLOCK) {
 463		*rtblock = r;
 464		return 0;
 465	}
 466	bbno = XFS_BITTOBLOCK(mp, bno);
 467	i = 0;
 468	ASSERT(minlen != 0);
 469	log2len = xfs_highbit32(minlen);
 470	/*
 471	 * Loop over all bitmap blocks (bbno + i is current block).
 472	 */
 473	for (;;) {
 474		/*
 475		 * Get summary information of extents of all useful levels
 476		 * starting in this bitmap block.
 477		 */
 478		error = xfs_rtany_summary(mp, tp, log2len, mp->m_rsumlevels - 1,
 479			bbno + i, rbpp, rsb, &any);
 480		if (error) {
 481			return error;
 482		}
 483		/*
 484		 * If there are any useful extents starting here, try
 485		 * allocating one.
 486		 */
 487		if (any) {
 488			/*
 489			 * On the positive side of the starting location.
 490			 */
 491			if (i >= 0) {
 492				/*
 493				 * Try to allocate an extent starting in
 494				 * this block.
 495				 */
 496				error = xfs_rtallocate_extent_block(mp, tp,
 497					bbno + i, minlen, maxlen, len, &n, rbpp,
 498					rsb, prod, &r);
 499				if (error) {
 500					return error;
 501				}
 502				/*
 503				 * If it worked, return it.
 504				 */
 505				if (r != NULLRTBLOCK) {
 506					*rtblock = r;
 507					return 0;
 508				}
 509			}
 510			/*
 511			 * On the negative side of the starting location.
 512			 */
 513			else {		/* i < 0 */
 514				/*
 515				 * Loop backwards through the bitmap blocks from
 516				 * the starting point-1 up to where we are now.
 517				 * There should be an extent which ends in this
 518				 * bitmap block and is long enough.
 519				 */
 520				for (j = -1; j > i; j--) {
 521					/*
 522					 * Grab the summary information for
 523					 * this bitmap block.
 524					 */
 525					error = xfs_rtany_summary(mp, tp,
 526						log2len, mp->m_rsumlevels - 1,
 527						bbno + j, rbpp, rsb, &any);
 528					if (error) {
 529						return error;
 530					}
 531					/*
 532					 * If there's no extent given in the
 533					 * summary that means the extent we
 534					 * found must carry over from an
 535					 * earlier block.  If there is an
 536					 * extent given, we've already tried
 537					 * that allocation, don't do it again.
 538					 */
 539					if (any)
 540						continue;
 541					error = xfs_rtallocate_extent_block(mp,
 542						tp, bbno + j, minlen, maxlen,
 543						len, &n, rbpp, rsb, prod, &r);
 544					if (error) {
 545						return error;
 546					}
 547					/*
 548					 * If it works, return the extent.
 549					 */
 550					if (r != NULLRTBLOCK) {
 551						*rtblock = r;
 552						return 0;
 553					}
 554				}
 555				/*
 556				 * There weren't intervening bitmap blocks
 557				 * with a long enough extent, or the
 558				 * allocation didn't work for some reason
 559				 * (i.e. it's a little * too short).
 560				 * Try to allocate from the summary block
 561				 * that we found.
 562				 */
 563				error = xfs_rtallocate_extent_block(mp, tp,
 564					bbno + i, minlen, maxlen, len, &n, rbpp,
 565					rsb, prod, &r);
 566				if (error) {
 567					return error;
 568				}
 569				/*
 570				 * If it works, return the extent.
 571				 */
 572				if (r != NULLRTBLOCK) {
 573					*rtblock = r;
 574					return 0;
 575				}
 576			}
 577		}
 578		/*
 579		 * Loop control.  If we were on the positive side, and there's
 580		 * still more blocks on the negative side, go there.
 581		 */
 582		if (i > 0 && (int)bbno - i >= 0)
 583			i = -i;
 584		/*
 585		 * If positive, and no more negative, but there are more
 586		 * positive, go there.
 587		 */
 588		else if (i > 0 && (int)bbno + i < mp->m_sb.sb_rbmblocks - 1)
 589			i++;
 590		/*
 591		 * If negative or 0 (just started), and there are positive
 592		 * blocks to go, go there.  The 0 case moves to block 1.
 593		 */
 594		else if (i <= 0 && (int)bbno - i < mp->m_sb.sb_rbmblocks - 1)
 595			i = 1 - i;
 596		/*
 597		 * If negative or 0 and there are more negative blocks,
 598		 * go there.
 599		 */
 600		else if (i <= 0 && (int)bbno + i > 0)
 601			i--;
 602		/*
 603		 * Must be done.  Return failure.
 604		 */
 605		else
 606			break;
 607	}
 608	*rtblock = NULLRTBLOCK;
 609	return 0;
 610}
 611
 612/*
 613 * Allocate an extent of length minlen<=len<=maxlen, with no position
 614 * specified.  If we don't get maxlen then use prod to trim
 615 * the length, if given.  The lengths are all in rtextents.
 616 */
 617STATIC int				/* error */
 618xfs_rtallocate_extent_size(
 619	xfs_mount_t	*mp,		/* file system mount point */
 620	xfs_trans_t	*tp,		/* transaction pointer */
 621	xfs_extlen_t	minlen,		/* minimum length to allocate */
 622	xfs_extlen_t	maxlen,		/* maximum length to allocate */
 623	xfs_extlen_t	*len,		/* out: actual length allocated */
 624	xfs_buf_t	**rbpp,		/* in/out: summary block buffer */
 625	xfs_fsblock_t	*rsb,		/* in/out: summary block number */
 626	xfs_extlen_t	prod,		/* extent product factor */
 627	xfs_rtblock_t	*rtblock)	/* out: start block allocated */
 628{
 629	int		error;		/* error value */
 630	int		i;		/* bitmap block number */
 631	int		l;		/* level number (loop control) */
 632	xfs_rtblock_t	n;		/* next block to be tried */
 633	xfs_rtblock_t	r;		/* result block number */
 634	xfs_suminfo_t	sum;		/* summary information for extents */
 635
 636	ASSERT(minlen % prod == 0 && maxlen % prod == 0);
 637	ASSERT(maxlen != 0);
 638
 639	/*
 640	 * Loop over all the levels starting with maxlen.
 641	 * At each level, look at all the bitmap blocks, to see if there
 642	 * are extents starting there that are long enough (>= maxlen).
 643	 * Note, only on the initial level can the allocation fail if
 644	 * the summary says there's an extent.
 645	 */
 646	for (l = xfs_highbit32(maxlen); l < mp->m_rsumlevels; l++) {
 647		/*
 648		 * Loop over all the bitmap blocks.
 649		 */
 650		for (i = 0; i < mp->m_sb.sb_rbmblocks; i++) {
 651			/*
 652			 * Get the summary for this level/block.
 653			 */
 654			error = xfs_rtget_summary(mp, tp, l, i, rbpp, rsb,
 655				&sum);
 656			if (error) {
 657				return error;
 658			}
 659			/*
 660			 * Nothing there, on to the next block.
 661			 */
 662			if (!sum)
 663				continue;
 664			/*
 665			 * Try allocating the extent.
 666			 */
 667			error = xfs_rtallocate_extent_block(mp, tp, i, maxlen,
 668				maxlen, len, &n, rbpp, rsb, prod, &r);
 669			if (error) {
 670				return error;
 671			}
 672			/*
 673			 * If it worked, return that.
 674			 */
 675			if (r != NULLRTBLOCK) {
 676				*rtblock = r;
 677				return 0;
 678			}
 679			/*
 680			 * If the "next block to try" returned from the
 681			 * allocator is beyond the next bitmap block,
 682			 * skip to that bitmap block.
 683			 */
 684			if (XFS_BITTOBLOCK(mp, n) > i + 1)
 685				i = XFS_BITTOBLOCK(mp, n) - 1;
 686		}
 687	}
 688	/*
 689	 * Didn't find any maxlen blocks.  Try smaller ones, unless
 690	 * we're asking for a fixed size extent.
 691	 */
 692	if (minlen > --maxlen) {
 693		*rtblock = NULLRTBLOCK;
 694		return 0;
 695	}
 696	ASSERT(minlen != 0);
 697	ASSERT(maxlen != 0);
 698
 699	/*
 700	 * Loop over sizes, from maxlen down to minlen.
 701	 * This time, when we do the allocations, allow smaller ones
 702	 * to succeed.
 703	 */
 704	for (l = xfs_highbit32(maxlen); l >= xfs_highbit32(minlen); l--) {
 705		/*
 706		 * Loop over all the bitmap blocks, try an allocation
 707		 * starting in that block.
 708		 */
 709		for (i = 0; i < mp->m_sb.sb_rbmblocks; i++) {
 710			/*
 711			 * Get the summary information for this level/block.
 712			 */
 713			error =	xfs_rtget_summary(mp, tp, l, i, rbpp, rsb,
 714						  &sum);
 715			if (error) {
 716				return error;
 717			}
 718			/*
 719			 * If nothing there, go on to next.
 720			 */
 721			if (!sum)
 722				continue;
 723			/*
 724			 * Try the allocation.  Make sure the specified
 725			 * minlen/maxlen are in the possible range for
 726			 * this summary level.
 727			 */
 728			error = xfs_rtallocate_extent_block(mp, tp, i,
 729					XFS_RTMAX(minlen, 1 << l),
 730					XFS_RTMIN(maxlen, (1 << (l + 1)) - 1),
 731					len, &n, rbpp, rsb, prod, &r);
 732			if (error) {
 733				return error;
 734			}
 735			/*
 736			 * If it worked, return that extent.
 737			 */
 738			if (r != NULLRTBLOCK) {
 739				*rtblock = r;
 740				return 0;
 741			}
 742			/*
 743			 * If the "next block to try" returned from the
 744			 * allocator is beyond the next bitmap block,
 745			 * skip to that bitmap block.
 746			 */
 747			if (XFS_BITTOBLOCK(mp, n) > i + 1)
 748				i = XFS_BITTOBLOCK(mp, n) - 1;
 749		}
 750	}
 751	/*
 752	 * Got nothing, return failure.
 753	 */
 754	*rtblock = NULLRTBLOCK;
 755	return 0;
 756}
 757
 758/*
 759 * Allocate space to the bitmap or summary file, and zero it, for growfs.
 760 */
 761STATIC int
 762xfs_growfs_rt_alloc(
 763	struct xfs_mount	*mp,		/* file system mount point */
 764	xfs_extlen_t		oblocks,	/* old count of blocks */
 765	xfs_extlen_t		nblocks,	/* new count of blocks */
 766	struct xfs_inode	*ip)		/* inode (bitmap/summary) */
 767{
 768	xfs_fileoff_t		bno;		/* block number in file */
 769	struct xfs_buf		*bp;	/* temporary buffer for zeroing */
 770	xfs_daddr_t		d;		/* disk block address */
 771	int			error;		/* error return value */
 772	xfs_fsblock_t		firstblock;/* first block allocated in xaction */
 773	struct xfs_defer_ops	dfops;		/* list of freed blocks */
 774	xfs_fsblock_t		fsbno;		/* filesystem block for bno */
 775	struct xfs_bmbt_irec	map;		/* block map output */
 776	int			nmap;		/* number of block maps */
 777	int			resblks;	/* space reservation */
 778	struct xfs_trans	*tp;
 779
 780	/*
 781	 * Allocate space to the file, as necessary.
 782	 */
 783	while (oblocks < nblocks) {
 784		resblks = XFS_GROWFSRT_SPACE_RES(mp, nblocks - oblocks);
 785		/*
 786		 * Reserve space & log for one extent added to the file.
 787		 */
 788		error = xfs_trans_alloc(mp, &M_RES(mp)->tr_growrtalloc, resblks,
 789				0, 0, &tp);
 790		if (error)
 791			return error;
 792		/*
 793		 * Lock the inode.
 794		 */
 795		xfs_ilock(ip, XFS_ILOCK_EXCL);
 796		xfs_trans_ijoin(tp, ip, XFS_ILOCK_EXCL);
 797
 798		xfs_defer_init(&dfops, &firstblock);
 799		/*
 800		 * Allocate blocks to the bitmap file.
 801		 */
 802		nmap = 1;
 803		error = xfs_bmapi_write(tp, ip, oblocks, nblocks - oblocks,
 804					XFS_BMAPI_METADATA, &firstblock,
 805					resblks, &map, &nmap, &dfops);
 806		if (!error && nmap < 1)
 807			error = -ENOSPC;
 808		if (error)
 809			goto out_bmap_cancel;
 810		/*
 811		 * Free any blocks freed up in the transaction, then commit.
 812		 */
 813		error = xfs_defer_finish(&tp, &dfops, NULL);
 814		if (error)
 815			goto out_bmap_cancel;
 816		error = xfs_trans_commit(tp);
 817		if (error)
 818			return error;
 819		/*
 820		 * Now we need to clear the allocated blocks.
 821		 * Do this one block per transaction, to keep it simple.
 822		 */
 823		for (bno = map.br_startoff, fsbno = map.br_startblock;
 824		     bno < map.br_startoff + map.br_blockcount;
 825		     bno++, fsbno++) {
 826			/*
 827			 * Reserve log for one block zeroing.
 828			 */
 829			error = xfs_trans_alloc(mp, &M_RES(mp)->tr_growrtzero,
 830					0, 0, 0, &tp);
 831			if (error)
 832				return error;
 833			/*
 834			 * Lock the bitmap inode.
 835			 */
 836			xfs_ilock(ip, XFS_ILOCK_EXCL);
 837			xfs_trans_ijoin(tp, ip, XFS_ILOCK_EXCL);
 838			/*
 839			 * Get a buffer for the block.
 840			 */
 841			d = XFS_FSB_TO_DADDR(mp, fsbno);
 842			bp = xfs_trans_get_buf(tp, mp->m_ddev_targp, d,
 843				mp->m_bsize, 0);
 844			if (bp == NULL) {
 845				error = -EIO;
 846				goto out_trans_cancel;
 847			}
 848			memset(bp->b_addr, 0, mp->m_sb.sb_blocksize);
 849			xfs_trans_log_buf(tp, bp, 0, mp->m_sb.sb_blocksize - 1);
 850			/*
 851			 * Commit the transaction.
 852			 */
 853			error = xfs_trans_commit(tp);
 854			if (error)
 855				return error;
 856		}
 857		/*
 858		 * Go on to the next extent, if any.
 859		 */
 860		oblocks = map.br_startoff + map.br_blockcount;
 861	}
 862
 863	return 0;
 864
 865out_bmap_cancel:
 866	xfs_defer_cancel(&dfops);
 867out_trans_cancel:
 868	xfs_trans_cancel(tp);
 869	return error;
 870}
 871
 872/*
 873 * Visible (exported) functions.
 874 */
 875
 876/*
 877 * Grow the realtime area of the filesystem.
 878 */
 879int
 880xfs_growfs_rt(
 881	xfs_mount_t	*mp,		/* mount point for filesystem */
 882	xfs_growfs_rt_t	*in)		/* growfs rt input struct */
 883{
 884	xfs_rtblock_t	bmbno;		/* bitmap block number */
 885	xfs_buf_t	*bp;		/* temporary buffer */
 886	int		error;		/* error return value */
 887	xfs_mount_t	*nmp;		/* new (fake) mount structure */
 888	xfs_rfsblock_t	nrblocks;	/* new number of realtime blocks */
 889	xfs_extlen_t	nrbmblocks;	/* new number of rt bitmap blocks */
 890	xfs_rtblock_t	nrextents;	/* new number of realtime extents */
 891	uint8_t		nrextslog;	/* new log2 of sb_rextents */
 892	xfs_extlen_t	nrsumblocks;	/* new number of summary blocks */
 893	uint		nrsumlevels;	/* new rt summary levels */
 894	uint		nrsumsize;	/* new size of rt summary, bytes */
 895	xfs_sb_t	*nsbp;		/* new superblock */
 896	xfs_extlen_t	rbmblocks;	/* current number of rt bitmap blocks */
 897	xfs_extlen_t	rsumblocks;	/* current number of rt summary blks */
 898	xfs_sb_t	*sbp;		/* old superblock */
 899	xfs_fsblock_t	sumbno;		/* summary block number */
 900
 901	sbp = &mp->m_sb;
 902	/*
 903	 * Initial error checking.
 904	 */
 905	if (!capable(CAP_SYS_ADMIN))
 906		return -EPERM;
 907	if (mp->m_rtdev_targp == NULL || mp->m_rbmip == NULL ||
 908	    (nrblocks = in->newblocks) <= sbp->sb_rblocks ||
 909	    (sbp->sb_rblocks && (in->extsize != sbp->sb_rextsize)))
 910		return -EINVAL;
 911	if ((error = xfs_sb_validate_fsb_count(sbp, nrblocks)))
 912		return error;
 913	/*
 914	 * Read in the last block of the device, make sure it exists.
 915	 */
 916	error = xfs_buf_read_uncached(mp->m_rtdev_targp,
 917				XFS_FSB_TO_BB(mp, nrblocks - 1),
 918				XFS_FSB_TO_BB(mp, 1), 0, &bp, NULL);
 919	if (error)
 920		return error;
 921	xfs_buf_relse(bp);
 922
 923	/*
 924	 * Calculate new parameters.  These are the final values to be reached.
 925	 */
 926	nrextents = nrblocks;
 927	do_div(nrextents, in->extsize);
 928	nrbmblocks = howmany_64(nrextents, NBBY * sbp->sb_blocksize);
 929	nrextslog = xfs_highbit32(nrextents);
 930	nrsumlevels = nrextslog + 1;
 931	nrsumsize = (uint)sizeof(xfs_suminfo_t) * nrsumlevels * nrbmblocks;
 932	nrsumblocks = XFS_B_TO_FSB(mp, nrsumsize);
 933	nrsumsize = XFS_FSB_TO_B(mp, nrsumblocks);
 934	/*
 935	 * New summary size can't be more than half the size of
 936	 * the log.  This prevents us from getting a log overflow,
 937	 * since we'll log basically the whole summary file at once.
 938	 */
 939	if (nrsumblocks > (mp->m_sb.sb_logblocks >> 1))
 940		return -EINVAL;
 941	/*
 942	 * Get the old block counts for bitmap and summary inodes.
 943	 * These can't change since other growfs callers are locked out.
 944	 */
 945	rbmblocks = XFS_B_TO_FSB(mp, mp->m_rbmip->i_d.di_size);
 946	rsumblocks = XFS_B_TO_FSB(mp, mp->m_rsumip->i_d.di_size);
 947	/*
 948	 * Allocate space to the bitmap and summary files, as necessary.
 949	 */
 950	error = xfs_growfs_rt_alloc(mp, rbmblocks, nrbmblocks, mp->m_rbmip);
 951	if (error)
 952		return error;
 953	error = xfs_growfs_rt_alloc(mp, rsumblocks, nrsumblocks, mp->m_rsumip);
 954	if (error)
 955		return error;
 956	/*
 957	 * Allocate a new (fake) mount/sb.
 958	 */
 959	nmp = kmem_alloc(sizeof(*nmp), KM_SLEEP);
 960	/*
 961	 * Loop over the bitmap blocks.
 962	 * We will do everything one bitmap block at a time.
 963	 * Skip the current block if it is exactly full.
 964	 * This also deals with the case where there were no rtextents before.
 965	 */
 966	for (bmbno = sbp->sb_rbmblocks -
 967		     ((sbp->sb_rextents & ((1 << mp->m_blkbit_log) - 1)) != 0);
 968	     bmbno < nrbmblocks;
 969	     bmbno++) {
 970		xfs_trans_t	*tp;
 971
 972		*nmp = *mp;
 973		nsbp = &nmp->m_sb;
 974		/*
 975		 * Calculate new sb and mount fields for this round.
 976		 */
 977		nsbp->sb_rextsize = in->extsize;
 978		nsbp->sb_rbmblocks = bmbno + 1;
 979		nsbp->sb_rblocks =
 980			XFS_RTMIN(nrblocks,
 981				  nsbp->sb_rbmblocks * NBBY *
 982				  nsbp->sb_blocksize * nsbp->sb_rextsize);
 983		nsbp->sb_rextents = nsbp->sb_rblocks;
 984		do_div(nsbp->sb_rextents, nsbp->sb_rextsize);
 985		ASSERT(nsbp->sb_rextents != 0);
 986		nsbp->sb_rextslog = xfs_highbit32(nsbp->sb_rextents);
 987		nrsumlevels = nmp->m_rsumlevels = nsbp->sb_rextslog + 1;
 988		nrsumsize =
 989			(uint)sizeof(xfs_suminfo_t) * nrsumlevels *
 990			nsbp->sb_rbmblocks;
 991		nrsumblocks = XFS_B_TO_FSB(mp, nrsumsize);
 992		nmp->m_rsumsize = nrsumsize = XFS_FSB_TO_B(mp, nrsumblocks);
 993		/*
 994		 * Start a transaction, get the log reservation.
 995		 */
 996		error = xfs_trans_alloc(mp, &M_RES(mp)->tr_growrtfree, 0, 0, 0,
 997				&tp);
 998		if (error)
 999			break;
1000		/*
1001		 * Lock out other callers by grabbing the bitmap inode lock.
1002		 */
1003		xfs_ilock(mp->m_rbmip, XFS_ILOCK_EXCL);
1004		xfs_trans_ijoin(tp, mp->m_rbmip, XFS_ILOCK_EXCL);
1005		/*
1006		 * Update the bitmap inode's size.
1007		 */
1008		mp->m_rbmip->i_d.di_size =
1009			nsbp->sb_rbmblocks * nsbp->sb_blocksize;
1010		xfs_trans_log_inode(tp, mp->m_rbmip, XFS_ILOG_CORE);
1011		/*
1012		 * Get the summary inode into the transaction.
1013		 */
1014		xfs_ilock(mp->m_rsumip, XFS_ILOCK_EXCL);
1015		xfs_trans_ijoin(tp, mp->m_rsumip, XFS_ILOCK_EXCL);
1016		/*
1017		 * Update the summary inode's size.
1018		 */
1019		mp->m_rsumip->i_d.di_size = nmp->m_rsumsize;
1020		xfs_trans_log_inode(tp, mp->m_rsumip, XFS_ILOG_CORE);
1021		/*
1022		 * Copy summary data from old to new sizes.
1023		 * Do this when the real size (not block-aligned) changes.
1024		 */
1025		if (sbp->sb_rbmblocks != nsbp->sb_rbmblocks ||
1026		    mp->m_rsumlevels != nmp->m_rsumlevels) {
1027			error = xfs_rtcopy_summary(mp, nmp, tp);
1028			if (error)
1029				goto error_cancel;
1030		}
1031		/*
1032		 * Update superblock fields.
1033		 */
1034		if (nsbp->sb_rextsize != sbp->sb_rextsize)
1035			xfs_trans_mod_sb(tp, XFS_TRANS_SB_REXTSIZE,
1036				nsbp->sb_rextsize - sbp->sb_rextsize);
1037		if (nsbp->sb_rbmblocks != sbp->sb_rbmblocks)
1038			xfs_trans_mod_sb(tp, XFS_TRANS_SB_RBMBLOCKS,
1039				nsbp->sb_rbmblocks - sbp->sb_rbmblocks);
1040		if (nsbp->sb_rblocks != sbp->sb_rblocks)
1041			xfs_trans_mod_sb(tp, XFS_TRANS_SB_RBLOCKS,
1042				nsbp->sb_rblocks - sbp->sb_rblocks);
1043		if (nsbp->sb_rextents != sbp->sb_rextents)
1044			xfs_trans_mod_sb(tp, XFS_TRANS_SB_REXTENTS,
1045				nsbp->sb_rextents - sbp->sb_rextents);
1046		if (nsbp->sb_rextslog != sbp->sb_rextslog)
1047			xfs_trans_mod_sb(tp, XFS_TRANS_SB_REXTSLOG,
1048				nsbp->sb_rextslog - sbp->sb_rextslog);
1049		/*
1050		 * Free new extent.
1051		 */
1052		bp = NULL;
1053		error = xfs_rtfree_range(nmp, tp, sbp->sb_rextents,
1054			nsbp->sb_rextents - sbp->sb_rextents, &bp, &sumbno);
1055		if (error) {
1056error_cancel:
1057			xfs_trans_cancel(tp);
1058			break;
1059		}
1060		/*
1061		 * Mark more blocks free in the superblock.
1062		 */
1063		xfs_trans_mod_sb(tp, XFS_TRANS_SB_FREXTENTS,
1064			nsbp->sb_rextents - sbp->sb_rextents);
1065		/*
1066		 * Update mp values into the real mp structure.
1067		 */
1068		mp->m_rsumlevels = nrsumlevels;
1069		mp->m_rsumsize = nrsumsize;
1070
1071		error = xfs_trans_commit(tp);
1072		if (error)
1073			break;
1074	}
1075
1076	/*
1077	 * Free the fake mp structure.
1078	 */
1079	kmem_free(nmp);
1080
1081	return error;
1082}
1083
1084/*
1085 * Allocate an extent in the realtime subvolume, with the usual allocation
1086 * parameters.  The length units are all in realtime extents, as is the
1087 * result block number.
1088 */
1089int					/* error */
1090xfs_rtallocate_extent(
1091	xfs_trans_t	*tp,		/* transaction pointer */
1092	xfs_rtblock_t	bno,		/* starting block number to allocate */
1093	xfs_extlen_t	minlen,		/* minimum length to allocate */
1094	xfs_extlen_t	maxlen,		/* maximum length to allocate */
1095	xfs_extlen_t	*len,		/* out: actual length allocated */
1096	int		wasdel,		/* was a delayed allocation extent */
1097	xfs_extlen_t	prod,		/* extent product factor */
1098	xfs_rtblock_t	*rtblock)	/* out: start block allocated */
1099{
1100	xfs_mount_t	*mp = tp->t_mountp;
1101	int		error;		/* error value */
1102	xfs_rtblock_t	r;		/* result allocated block */
1103	xfs_fsblock_t	sb;		/* summary file block number */
1104	xfs_buf_t	*sumbp;		/* summary file block buffer */
1105
1106	ASSERT(xfs_isilocked(mp->m_rbmip, XFS_ILOCK_EXCL));
1107	ASSERT(minlen > 0 && minlen <= maxlen);
1108
1109	/*
1110	 * If prod is set then figure out what to do to minlen and maxlen.
1111	 */
1112	if (prod > 1) {
1113		xfs_extlen_t	i;
1114
1115		if ((i = maxlen % prod))
1116			maxlen -= i;
1117		if ((i = minlen % prod))
1118			minlen += prod - i;
1119		if (maxlen < minlen) {
1120			*rtblock = NULLRTBLOCK;
1121			return 0;
1122		}
1123	}
1124
1125retry:
1126	sumbp = NULL;
1127	if (bno == 0) {
1128		error = xfs_rtallocate_extent_size(mp, tp, minlen, maxlen, len,
1129				&sumbp,	&sb, prod, &r);
1130	} else {
1131		error = xfs_rtallocate_extent_near(mp, tp, bno, minlen, maxlen,
1132				len, &sumbp, &sb, prod, &r);
1133	}
1134
1135	if (error)
1136		return error;
1137
1138	/*
1139	 * If it worked, update the superblock.
1140	 */
1141	if (r != NULLRTBLOCK) {
1142		long	slen = (long)*len;
1143
1144		ASSERT(*len >= minlen && *len <= maxlen);
1145		if (wasdel)
1146			xfs_trans_mod_sb(tp, XFS_TRANS_SB_RES_FREXTENTS, -slen);
1147		else
1148			xfs_trans_mod_sb(tp, XFS_TRANS_SB_FREXTENTS, -slen);
1149	} else if (prod > 1) {
1150		prod = 1;
1151		goto retry;
1152	}
1153
1154	*rtblock = r;
1155	return 0;
1156}
1157
1158/*
1159 * Initialize realtime fields in the mount structure.
1160 */
1161int				/* error */
1162xfs_rtmount_init(
1163	struct xfs_mount	*mp)	/* file system mount structure */
1164{
1165	struct xfs_buf		*bp;	/* buffer for last block of subvolume */
1166	struct xfs_sb		*sbp;	/* filesystem superblock copy in mount */
1167	xfs_daddr_t		d;	/* address of last block of subvolume */
1168	int			error;
1169
1170	sbp = &mp->m_sb;
1171	if (sbp->sb_rblocks == 0)
1172		return 0;
1173	if (mp->m_rtdev_targp == NULL) {
1174		xfs_warn(mp,
1175	"Filesystem has a realtime volume, use rtdev=device option");
1176		return -ENODEV;
1177	}
1178	mp->m_rsumlevels = sbp->sb_rextslog + 1;
1179	mp->m_rsumsize =
1180		(uint)sizeof(xfs_suminfo_t) * mp->m_rsumlevels *
1181		sbp->sb_rbmblocks;
1182	mp->m_rsumsize = roundup(mp->m_rsumsize, sbp->sb_blocksize);
1183	mp->m_rbmip = mp->m_rsumip = NULL;
1184	/*
1185	 * Check that the realtime section is an ok size.
1186	 */
1187	d = (xfs_daddr_t)XFS_FSB_TO_BB(mp, mp->m_sb.sb_rblocks);
1188	if (XFS_BB_TO_FSB(mp, d) != mp->m_sb.sb_rblocks) {
1189		xfs_warn(mp, "realtime mount -- %llu != %llu",
1190			(unsigned long long) XFS_BB_TO_FSB(mp, d),
1191			(unsigned long long) mp->m_sb.sb_rblocks);
1192		return -EFBIG;
1193	}
1194	error = xfs_buf_read_uncached(mp->m_rtdev_targp,
1195					d - XFS_FSB_TO_BB(mp, 1),
1196					XFS_FSB_TO_BB(mp, 1), 0, &bp, NULL);
1197	if (error) {
1198		xfs_warn(mp, "realtime device size check failed");
1199		return error;
1200	}
1201	xfs_buf_relse(bp);
1202	return 0;
1203}
1204
1205/*
1206 * Get the bitmap and summary inodes into the mount structure
1207 * at mount time.
1208 */
1209int					/* error */
1210xfs_rtmount_inodes(
1211	xfs_mount_t	*mp)		/* file system mount structure */
1212{
1213	int		error;		/* error return value */
1214	xfs_sb_t	*sbp;
1215
1216	sbp = &mp->m_sb;
1217	if (sbp->sb_rbmino == NULLFSINO)
1218		return 0;
1219	error = xfs_iget(mp, NULL, sbp->sb_rbmino, 0, 0, &mp->m_rbmip);
1220	if (error)
1221		return error;
1222	ASSERT(mp->m_rbmip != NULL);
1223	ASSERT(sbp->sb_rsumino != NULLFSINO);
1224	error = xfs_iget(mp, NULL, sbp->sb_rsumino, 0, 0, &mp->m_rsumip);
1225	if (error) {
1226		IRELE(mp->m_rbmip);
1227		return error;
1228	}
1229	ASSERT(mp->m_rsumip != NULL);
1230	return 0;
1231}
1232
1233void
1234xfs_rtunmount_inodes(
1235	struct xfs_mount	*mp)
1236{
1237	if (mp->m_rbmip)
1238		IRELE(mp->m_rbmip);
1239	if (mp->m_rsumip)
1240		IRELE(mp->m_rsumip);
1241}
1242
1243/*
1244 * Pick an extent for allocation at the start of a new realtime file.
1245 * Use the sequence number stored in the atime field of the bitmap inode.
1246 * Translate this to a fraction of the rtextents, and return the product
1247 * of rtextents and the fraction.
1248 * The fraction sequence is 0, 1/2, 1/4, 3/4, 1/8, ..., 7/8, 1/16, ...
1249 */
1250int					/* error */
1251xfs_rtpick_extent(
1252	xfs_mount_t	*mp,		/* file system mount point */
1253	xfs_trans_t	*tp,		/* transaction pointer */
1254	xfs_extlen_t	len,		/* allocation length (rtextents) */
1255	xfs_rtblock_t	*pick)		/* result rt extent */
1256{
1257	xfs_rtblock_t	b;		/* result block */
1258	int		log2;		/* log of sequence number */
1259	uint64_t	resid;		/* residual after log removed */
1260	uint64_t	seq;		/* sequence number of file creation */
1261	uint64_t	*seqp;		/* pointer to seqno in inode */
1262
1263	ASSERT(xfs_isilocked(mp->m_rbmip, XFS_ILOCK_EXCL));
1264
1265	seqp = (uint64_t *)&VFS_I(mp->m_rbmip)->i_atime;
1266	if (!(mp->m_rbmip->i_d.di_flags & XFS_DIFLAG_NEWRTBM)) {
1267		mp->m_rbmip->i_d.di_flags |= XFS_DIFLAG_NEWRTBM;
1268		*seqp = 0;
1269	}
1270	seq = *seqp;
1271	if ((log2 = xfs_highbit64(seq)) == -1)
1272		b = 0;
1273	else {
1274		resid = seq - (1ULL << log2);
1275		b = (mp->m_sb.sb_rextents * ((resid << 1) + 1ULL)) >>
1276		    (log2 + 1);
1277		if (b >= mp->m_sb.sb_rextents)
1278			b = do_mod(b, mp->m_sb.sb_rextents);
1279		if (b + len > mp->m_sb.sb_rextents)
1280			b = mp->m_sb.sb_rextents - len;
1281	}
1282	*seqp = seq + 1;
1283	xfs_trans_log_inode(tp, mp->m_rbmip, XFS_ILOG_CORE);
1284	*pick = b;
1285	return 0;
1286}