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fs/jfs: TRIM support for JFS Filesystem

From:  Tino Reichardt <list-linux-fsdevel@mcmilk.de>
To:  linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, jfs-discussion@lists.sourceforge.net
Subject:  [PATCH] fs/jfs: TRIM support for JFS Filesystem
Date:  Thu, 26 Jul 2012 23:32:19 +0200
Message-ID:  <20120726213219.GA28330@mcmilk.de>
Archive-link:  Article

This patch adds support for the two linux interfaces of the discard/TRIM
command for SSD devices and sparse/thinly-provisioned LUNs.

JFS will support batched discard via FITRIM ioctl and online discard
with the discard mount option.

I also think that a short description of the FITRIM ioctl should it made
into Documetation/ioctl/fitrim.txt - but that would be part of some
other patch. Maybe from Lukas Czerner?

For the online discard, you can also specify the minimum number of
blocks. Everything of it is described in
Documentation/filesystems/jfs.txt... so I am not writing it again in
that mail.

So than, maybe some other can stress-test JFS on some SSD as well?


Signed-off-by: Tino Reichardt <list-jfs@mcmilk.de>

PS: Sorry for my bad english ;)

-- 
regards, TR
diff -X exclude -urpN linux-git/Documentation/filesystems/jfs.txt linux_jfs-trim/Documentation/filesystems/jfs.txt
--- linux-git/Documentation/filesystems/jfs.txt	2011-03-01 10:22:59.000000000 +0100
+++ linux_jfs-trim/Documentation/filesystems/jfs.txt	2012-07-26 22:52:33.244721671 +0200
@@ -3,6 +3,7 @@ IBM's Journaled File System (JFS) for Li
 JFS Homepage:  http://jfs.sourceforge.net/
 
 The following mount options are supported:
+(*) == default
 
 iocharset=name	Character set to use for converting from Unicode to
 		ASCII.  The default is to do no conversion.  Use
@@ -21,12 +22,12 @@ nointegrity	Do not write to the journal.
 		from backup media.  The integrity of the volume is not
 		guaranteed if the system abnormally abends.
 
-integrity	Default.  Commit metadata changes to the journal.  Use this
+integrity(*)	Default.  Commit metadata changes to the journal.  Use this
 		option to remount a volume where the nointegrity option was
 		previously specified in order to restore normal behavior.
 
 errors=continue		Keep going on a filesystem error.
-errors=remount-ro	Default. Remount the filesystem read-only on an error.
+errors=remount-ro(*)	Default. Remount the filesystem read-only on an error.
 errors=panic		Panic and halt the machine if an error occurs.
 
 uid=value	Override on-disk uid with specified value
@@ -35,6 +36,18 @@ umask=value	Override on-disk umask with
 		directories, the execute bit will be set if the corresponding
 		read bit is set.
 
+discard=minlen	This enables/disables the use of discard/TRIM commands.
+discard		The discard/TRIM commands are sent to the underlying
+nodiscard(*)	block device when blocks are freed. This is useful for SSD
+		devices and sparse/thinly-provisioned LUNs.  The FITRIM ioctl
+		command is also available together with the nodiscard option.
+		The value of minlen specifies the minimum blockcount, when
+		a TRIM command to the block device is considered usefull.
+		When no value is given to the discard option, it defaults to
+		64 blocks, which means 256KiB in JFS.
+		The minlen value of discard overrides the minlen value given
+		on an FITRIM ioctl().
+
 Please send bugs, comments, cards and letters to shaggy@linux.vnet.ibm.com.
 
 The JFS mailing list can be subscribed to by using the link labeled
diff -X exclude -urpN linux-git/fs/jfs/Makefile linux_jfs-trim/fs/jfs/Makefile
--- linux-git/fs/jfs/Makefile	2011-08-17 07:31:10.000000000 +0200
+++ linux_jfs-trim/fs/jfs/Makefile	2012-07-26 22:53:48.640979880 +0200
@@ -6,7 +6,7 @@ obj-$(CONFIG_JFS_FS) += jfs.o
 
 jfs-y    := super.o file.o inode.o namei.o jfs_mount.o jfs_umount.o \
 	    jfs_xtree.o jfs_imap.o jfs_debug.o jfs_dmap.o \
-	    jfs_unicode.o jfs_dtree.o jfs_inode.o \
+	    jfs_unicode.o jfs_dtree.o jfs_inode.o jfs_discard.o \
 	    jfs_extent.o symlink.o jfs_metapage.o \
 	    jfs_logmgr.o jfs_txnmgr.o jfs_uniupr.o \
 	    resize.o xattr.o ioctl.o
diff -X exclude -urpN linux-git/fs/jfs/ioctl.c linux_jfs-trim/fs/jfs/ioctl.c
--- linux-git/fs/jfs/ioctl.c	2012-01-10 19:31:59.000000000 +0100
+++ linux_jfs-trim/fs/jfs/ioctl.c	2012-07-26 22:53:48.640979880 +0200
@@ -11,13 +11,17 @@
 #include <linux/mount.h>
 #include <linux/time.h>
 #include <linux/sched.h>
+#include <linux/blkdev.h>
 #include <asm/current.h>
 #include <asm/uaccess.h>
 
+#include "jfs_filsys.h"
+#include "jfs_debug.h"
 #include "jfs_incore.h"
 #include "jfs_dinode.h"
 #include "jfs_inode.h"
-
+#include "jfs_dmap.h"
+#include "jfs_discard.h"
 
 static struct {
 	long jfs_flag;
@@ -123,6 +127,40 @@ setflags_out:
 		mnt_drop_write_file(filp);
 		return err;
 	}
+
+	case FITRIM:
+	{
+		struct super_block *sb = inode->i_sb;
+		struct request_queue *q = bdev_get_queue(sb->s_bdev);
+		struct fstrim_range range;
+		s64 ret = 0;
+
+		if (!capable(CAP_SYS_ADMIN))
+			return -EPERM;
+
+		if (!blk_queue_discard(q)) {
+			jfs_warn("FITRIM not supported on device");
+			return -EOPNOTSUPP;
+		}
+
+		if (copy_from_user(&range, (struct fstrim_range __user *)arg,
+		    sizeof(range)))
+			return -EFAULT;
+
+		range.minlen = max((unsigned int)range.minlen,
+				   q->limits.discard_granularity);
+
+		ret = jfs_ioc_trim(inode, &range);
+		if (ret < 0)
+			return ret;
+
+		if (copy_to_user((struct fstrim_range __user *)arg, &range,
+		    sizeof(range)))
+			return -EFAULT;
+
+		return 0;
+	}
+
 	default:
 		return -ENOTTY;
 	}
@@ -142,6 +180,9 @@ long jfs_compat_ioctl(struct file *filp,
 	case JFS_IOC_SETFLAGS32:
 		cmd = JFS_IOC_SETFLAGS;
 		break;
+	case FITRIM:
+		cmd = FITRIM;
+		break;
 	}
 	return jfs_ioctl(filp, cmd, arg);
 }
diff -X exclude -urpN linux-git/fs/jfs/jfs_discard.c linux_jfs-trim/fs/jfs/jfs_discard.c
--- linux-git/fs/jfs/jfs_discard.c	1970-01-01 01:00:00.000000000 +0100
+++ linux_jfs-trim/fs/jfs/jfs_discard.c	2012-07-26 22:53:48.640979880 +0200
@@ -0,0 +1,119 @@
+/*
+ *   Copyright (C) Tino Reichardt, 2012
+ *
+ *   This program 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 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;  if not, write to the Free Software
+ *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+#include <linux/fs.h>
+#include <linux/slab.h>
+#include <linux/blkdev.h>
+
+#include "jfs_incore.h"
+#include "jfs_superblock.h"
+#include "jfs_dmap.h"
+#include "jfs_lock.h"
+#include "jfs_debug.h"
+
+
+/*
+ * NAME:	jfs_issue_discard()
+ *
+ * FUNCTION:	TRIM the specified block range on device, if supported
+ *
+ * PARAMETERS:
+ *	ip	- pointer to in-core inode
+ *	blkno	- starting block number to be trimmed (0..N)
+ *	nblocks	- number of blocks to be trimmed
+ *
+ * RETURN VALUES:
+ *	none
+ *
+ * serialization: IREAD_LOCK(ipbmap) held on entry/exit;
+ */
+void jfs_issue_discard(struct inode *ip, u64 blkno, u64 nblocks)
+{
+	struct super_block *sb = ip->i_sb;
+	int r = 0;
+
+	r = sb_issue_discard(sb, blkno, nblocks, GFP_NOFS, 0);
+	if (unlikely(r != 0)) {
+		printk(KERN_ERR "JFS: sb_issue_discard"
+			"(%p, %llu, %llu, GFP_NOFS, 0) = %d => failure!\n", sb,
+			(unsigned long long)blkno,
+			(unsigned long long)nblocks, r);
+	}
+
+#ifdef JFS_DEBUG_TRIM
+	printk(KERN_INFO "JFS: sb_issue_discard"
+		"(%p, %llu, %llu, GFP_NOFS, 0) = %d\n", sb,
+		(unsigned long long)blkno,
+		(unsigned long long)nblocks, r);
+#endif
+
+	return;
+}
+
+/*
+ * NAME:	jfs_ioc_trim()
+ *
+ * FUNCTION:	attempt to discard (TRIM) all free blocks from the
+ *              filesystem.
+ *
+ * PARAMETERS:
+ *	ip	- pointer to in-core inode;
+ *	range	- the range, given by user space
+ *
+ * RETURN VALUES:
+ *	0	- success
+ *	-EIO	- i/o error
+ */
+int jfs_ioc_trim(struct inode *ip, struct fstrim_range *range)
+{
+	struct inode *ipbmap = JFS_SBI(ip->i_sb)->ipbmap;
+	struct bmap *bmp = JFS_SBI(ip->i_sb)->bmap;
+	struct super_block *sb = ipbmap->i_sb;
+	int agno, agno_end;
+	s64 start, end, minlen;
+	u64 trimmed = 0;
+
+	/**
+	 * convert byte values to block size of filesystem:
+	 * start:	First Byte to trim
+	 * len:		number of Bytes to trim from start
+	 * minlen:	minimum extent length in Bytes
+	 */
+	start = range->start >> sb->s_blocksize_bits;
+	if (start < 0)
+		start = 0;
+	end = start + (range->len >> sb->s_blocksize_bits) - 1;
+	if (end >= bmp->db_mapsize)
+		end = bmp->db_mapsize - 1;
+	minlen = range->minlen >> sb->s_blocksize_bits;
+	if (minlen < 0)
+		minlen = 1;
+
+	/**
+	 * we trim all ag's within the range
+	 */
+	agno = BLKTOAG(start, JFS_SBI(ip->i_sb));
+	agno_end = BLKTOAG(end, JFS_SBI(ip->i_sb));
+	while (agno <= agno_end) {
+		trimmed += dbDiscardAG(ip, agno, minlen);
+		agno++;
+	}
+	range->len = trimmed << sb->s_blocksize_bits;
+
+	return 0;
+}
diff -X exclude -urpN linux-git/fs/jfs/jfs_discard.h linux_jfs-trim/fs/jfs/jfs_discard.h
--- linux-git/fs/jfs/jfs_discard.h	1970-01-01 01:00:00.000000000 +0100
+++ linux_jfs-trim/fs/jfs/jfs_discard.h	2012-07-26 22:53:48.640979880 +0200
@@ -0,0 +1,26 @@
+/*
+ *   Copyright (C) Tino Reichardt, 2012
+ *
+ *   This program 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 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;  if not, write to the Free Software
+ *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+#ifndef	_H_JFS_DISCARD
+#define _H_JFS_DISCARD
+
+struct fstrim_range;
+
+extern void jfs_issue_discard(struct inode *ip, u64 blkno, u64 nblocks);
+extern int jfs_ioc_trim(struct inode *ip, struct fstrim_range *range);
+
+#endif /* _H_JFS_DISCARD */
diff -X exclude -urpN linux-git/fs/jfs/jfs_dmap.c linux_jfs-trim/fs/jfs/jfs_dmap.c
--- linux-git/fs/jfs/jfs_dmap.c	2011-08-17 07:31:10.000000000 +0200
+++ linux_jfs-trim/fs/jfs/jfs_dmap.c	2012-07-26 22:53:48.644313195 +0200
@@ -1,5 +1,6 @@
 /*
  *   Copyright (C) International Business Machines Corp., 2000-2004
+ *   Portions Copyright (C) Tino Reichardt, 2012
  *
  *   This program is free software;  you can redistribute it and/or modify
  *   it under the terms of the GNU General Public License as published by
@@ -25,6 +26,7 @@
 #include "jfs_lock.h"
 #include "jfs_metapage.h"
 #include "jfs_debug.h"
+#include "jfs_discard.h"
 
 /*
  *	SERIALIZATION of the Block Allocation Map.
@@ -104,7 +106,6 @@ static int dbFreeBits(struct bmap * bmp,
 static int dbFreeDmap(struct bmap * bmp, struct dmap * dp, s64 blkno,
 		      int nblocks);
 static int dbMaxBud(u8 * cp);
-s64 dbMapFileSizeToMapSize(struct inode *ipbmap);
 static int blkstol2(s64 nb);
 
 static int cntlz(u32 value);
@@ -145,7 +146,6 @@ static const s8 budtab[256] = {
 	2, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, -1
 };
 
-
 /*
  * NAME:	dbMount()
  *
@@ -310,7 +310,6 @@ int dbSync(struct inode *ipbmap)
 	return (0);
 }
 
-
 /*
  * NAME:	dbFree()
  *
@@ -337,6 +336,7 @@ int dbFree(struct inode *ip, s64 blkno,
 	s64 lblkno, rem;
 	struct inode *ipbmap = JFS_SBI(ip->i_sb)->ipbmap;
 	struct bmap *bmp = JFS_SBI(ip->i_sb)->bmap;
+	struct super_block *sb = ipbmap->i_sb;
 
 	IREAD_LOCK(ipbmap, RDWRLOCK_DMAP);
 
@@ -351,6 +351,15 @@ int dbFree(struct inode *ip, s64 blkno,
 		return -EIO;
 	}
 
+	/**
+	 * TRIM the blocks, when mounted with discard option
+	 */
+	if (JFS_SBI(sb)->flag & JFS_DISCARD) {
+		if (JFS_SBI(sb)->minblks_trim <= nblocks) {
+			jfs_issue_discard(ipbmap, blkno, nblocks);
+		}
+	}
+
 	/*
 	 * free the blocks a dmap at a time.
 	 */
@@ -1095,7 +1104,6 @@ static int dbExtend(struct inode *ip, s6
 		/* we were not successful */
 		release_metapage(mp);
 
-
 	return (rc);
 }
 
@@ -1590,6 +1598,117 @@ static int dbAllocAny(struct bmap * bmp,
 
 
 /*
+ * NAME:	dbDiscardAG()
+ *
+ * FUNCTION:	attempt to discard (TRIM) all free blocks of specific AG
+ *
+ * 		algorithm:
+ * 		1) allocate blocks, as large as possible and save them
+ * 		2) trim all these saved block/length values
+ * 		3) mark the blocks free again
+ *
+ * 		benefit:
+ * 		- we work only on one ag at some time, which is fully blocked
+ * 		- reading / writing the fs is possible most time, even on trimming
+ *
+ * 		downside:
+ * 		- we write two times to the dmapctl and dmap pages
+ * 		- but for me, this seems the best way, better ideas?
+ * 		/TR 2012
+ *
+ * PARAMETERS:
+ *	ip	- pointer to in-core inode
+ *	agno	- ag to trim
+ *	minlen	- minimum value of contiguous blocks
+ *
+ * RETURN VALUES:
+ *	s64	- actual number of blocks trimmed
+ */
+s64 dbDiscardAG(struct inode *ip, int agno, s64 minlen)
+{
+	struct inode *ipbmap = JFS_SBI(ip->i_sb)->ipbmap;
+	struct bmap *bmp = JFS_SBI(ip->i_sb)->bmap;
+	s64 nblocks, blkno;
+	u64 trimmed = 0;
+	int rc, l2nb;
+	struct super_block *sb = ipbmap->i_sb;
+
+	struct range2trim {
+		u64 blkno;
+		u64 nblocks;
+	} *totrim, *tt;
+
+	/* max blkno / nblocks pairs to trim */
+	int count = 0, range_cnt = 32 * 1024;
+
+	/* prevent others from writing new stuff here, while trimming */
+	IWRITE_LOCK(ipbmap, RDWRLOCK_DMAP);
+
+	/* worst value: each free block gets an entry */
+	nblocks = bmp->db_agfree[agno];
+	totrim = kmalloc(sizeof(struct range2trim) * range_cnt, GFP_NOFS);
+	if (totrim == NULL) {
+		jfs_error(bmp->db_ipbmap->i_sb,
+			  "dbDiscardAG: no space for trim array");
+		IWRITE_UNLOCK(ipbmap);
+		return 0;
+	}
+
+	tt = totrim;
+	while (nblocks >= minlen) {
+		l2nb = BLKSTOL2(nblocks);
+
+		/* 0 = okay, -EIO = fatal, -ENOSPC -> block kleiner */
+		rc = dbAllocAG(bmp, agno, nblocks, l2nb, &blkno);
+		if (rc == 0) {
+			tt->blkno = blkno;
+			tt->nblocks = nblocks;
+			tt++; count++;
+
+#ifdef JFS_DEBUG_TRIM
+		printk(KERN_INFO "JFS: agno=%d/%d, blkno:%ld, nblocks=%ld\n",
+			agno+1, bmp->db_numag, (long int)blkno,
+			(long int)nblocks);
+#endif
+
+			/* the whole ag is free, trim now */
+			if (bmp->db_agfree[agno] == 0)
+				break;
+
+			/* give a hint for the next while */
+			nblocks = bmp->db_agfree[agno];
+			continue;
+		} else if (rc == -ENOSPC) {
+			/* search for next smaller log2 block */
+			l2nb = BLKSTOL2(nblocks) - 1;
+			nblocks = 1 << l2nb;
+		} else {
+			/* Trim any already-allocated blocks */
+			printk(KERN_ERR "JFS: dbDiscardAG: -EIO\n");
+			break;
+		}
+
+		/* check, if our trim array is full */
+		if (unlikely(count >= range_cnt - 1))
+			break;
+	}
+	IWRITE_UNLOCK(ipbmap);
+
+	tt->nblocks = 0; /* mark the current end */
+	for (tt = totrim; tt->nblocks != 0; tt++) {
+		if (!(JFS_SBI(sb)->flag & JFS_DISCARD)) {
+			/* not needed, when online discard is used */
+			jfs_issue_discard(ip, tt->blkno, tt->nblocks);
+		}
+		dbFree(ip, tt->blkno, tt->nblocks);
+		trimmed += tt->nblocks;
+	}
+	kfree(totrim);
+
+	return trimmed;
+}
+
+/*
  * NAME:	dbFindCtl()
  *
  * FUNCTION:	starting at a specified dmap control page level and block
diff -X exclude -urpN linux-git/fs/jfs/jfs_dmap.h linux_jfs-trim/fs/jfs/jfs_dmap.h
--- linux-git/fs/jfs/jfs_dmap.h	2011-08-17 07:31:10.000000000 +0200
+++ linux_jfs-trim/fs/jfs/jfs_dmap.h	2012-07-26 22:53:48.644313195 +0200
@@ -311,4 +311,6 @@ extern int dbAllocBottomUp(struct inode
 extern int dbExtendFS(struct inode *ipbmap, s64 blkno, s64 nblocks);
 extern void dbFinalizeBmap(struct inode *ipbmap);
 extern s64 dbMapFileSizeToMapSize(struct inode *ipbmap);
+extern s64 dbDiscardAG(struct inode *ip, int agno, s64 minlen);
+
 #endif				/* _H_JFS_DMAP */
diff -X exclude -urpN linux-git/fs/jfs/jfs_filsys.h linux_jfs-trim/fs/jfs/jfs_filsys.h
--- linux-git/fs/jfs/jfs_filsys.h	2011-08-17 07:31:10.000000000 +0200
+++ linux_jfs-trim/fs/jfs/jfs_filsys.h	2012-07-26 22:53:48.644313195 +0200
@@ -45,6 +45,9 @@
 /* mount time flag to disable journaling to disk */
 #define JFS_NOINTEGRITY 0x00000040
 
+/* mount time flag to enable TRIM to ssd disks */
+#define JFS_DISCARD     0x00000080
+
 /* commit option */
 #define	JFS_COMMIT	0x00000f00	/* commit option mask */
 #define	JFS_GROUPCOMMIT	0x00000100	/* group (of 1) commit */
diff -X exclude -urpN linux-git/fs/jfs/jfs_incore.h linux_jfs-trim/fs/jfs/jfs_incore.h
--- linux-git/fs/jfs/jfs_incore.h	2011-08-17 07:31:10.000000000 +0200
+++ linux_jfs-trim/fs/jfs/jfs_incore.h	2012-07-26 22:53:48.647646510 +0200
@@ -195,6 +195,7 @@ struct jfs_sb_info {
 	uint		uid;		/* uid to override on-disk uid */
 	uint		gid;		/* gid to override on-disk gid */
 	uint		umask;		/* umask to override on-disk umask */
+	uint		minblks_trim;	/* minimum blocks, for online trim */
 };
 
 /* jfs_sb_info commit_state */
diff -X exclude -urpN linux-git/fs/jfs/super.c linux_jfs-trim/fs/jfs/super.c
--- linux-git/fs/jfs/super.c	2012-07-24 21:31:28.000000000 +0200
+++ linux_jfs-trim/fs/jfs/super.c	2012-07-26 23:00:28.018816264 +0200
@@ -33,6 +33,7 @@
 #include <linux/slab.h>
 #include <asm/uaccess.h>
 #include <linux/seq_file.h>
+#include <linux/blkdev.h>
 
 #include "jfs_incore.h"
 #include "jfs_filsys.h"
@@ -197,7 +198,8 @@ static void jfs_put_super(struct super_b
 enum {
 	Opt_integrity, Opt_nointegrity, Opt_iocharset, Opt_resize,
 	Opt_resize_nosize, Opt_errors, Opt_ignore, Opt_err, Opt_quota,
-	Opt_usrquota, Opt_grpquota, Opt_uid, Opt_gid, Opt_umask
+	Opt_usrquota, Opt_grpquota, Opt_uid, Opt_gid, Opt_umask,
+	Opt_discard, Opt_nodiscard, Opt_discard_minblk
 };
 
 static const match_table_t tokens = {
@@ -214,6 +216,9 @@ static const match_table_t tokens = {
 	{Opt_uid, "uid=%u"},
 	{Opt_gid, "gid=%u"},
 	{Opt_umask, "umask=%u"},
+	{Opt_discard, "discard"},
+	{Opt_nodiscard, "nodiscard"},
+	{Opt_discard_minblk, "discard=%u"},
 	{Opt_err, NULL}
 };
 
@@ -324,12 +329,14 @@ static int parse_options(char *options,
 			sbi->uid = simple_strtoul(uid, &uid, 0);
 			break;
 		}
+
 		case Opt_gid:
 		{
 			char *gid = args[0].from;
 			sbi->gid = simple_strtoul(gid, &gid, 0);
 			break;
 		}
+
 		case Opt_umask:
 		{
 			char *umask = args[0].from;
@@ -341,6 +348,43 @@ static int parse_options(char *options,
 			}
 			break;
 		}
+
+		case Opt_discard:
+		{
+			struct request_queue *q = bdev_get_queue(sb->s_bdev);
+			/* if set to 1, even copying files will cause
+			 * trimming :O
+			 * -> user has more control over the online trimming
+			 */
+			sbi->minblks_trim = 64;
+			if (blk_queue_discard(q)) {
+				*flag |= JFS_DISCARD;
+			} else {
+				printk(KERN_ERR "JFS: discard option "
+					"not supported on device\n");
+			}
+			break;
+		}
+
+		case Opt_nodiscard:
+			*flag &= ~JFS_DISCARD;
+			break;
+
+		case Opt_discard_minblk:
+		{
+			struct request_queue *q = bdev_get_queue(sb->s_bdev);
+			char *minblks_trim = args[0].from;
+			if (blk_queue_discard(q)) {
+				*flag |= JFS_DISCARD;
+				sbi->minblks_trim = simple_strtoull(
+					minblks_trim, &minblks_trim, 0);
+			} else {
+				printk(KERN_ERR "JFS: discard option "
+					"not supported on device\n");
+			}
+			break;
+		}
+
 		default:
 			printk("jfs: Unrecognized mount option \"%s\" "
 					" or missing value\n", p);
@@ -625,6 +669,8 @@ static int jfs_show_options(struct seq_f
 		seq_printf(seq, ",umask=%03o", sbi->umask);
 	if (sbi->flag & JFS_NOINTEGRITY)
 		seq_puts(seq, ",nointegrity");
+	if (sbi->flag & JFS_DISCARD)
+		seq_printf(seq, ",discard=%u", sbi->minblks_trim);
 	if (sbi->nls_tab)
 		seq_printf(seq, ",iocharset=%s", sbi->nls_tab->charset);
 	if (sbi->flag & JFS_ERR_CONTINUE)


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