12 files changed, 199 insertions, 116 deletions

diff --git a/Documentation/filesystems/nilfs2.txt b/Documentation/filesystems/nilfs2.txt
index 839efd8a8a8c..cf6d0d85ca82 100644
--- a/Documentation/filesystems/nilfs2.txt
+++ b/Documentation/filesystems/nilfs2.txt
@@ -74,6 +74,9 @@ norecovery		Disable recovery of the filesystem on mount.
                         This disables every write access on the device for
                         read-only mounts or snapshots.  This option will fail
                         for r/w mounts on an unclean volume.
+discard                 Issue discard/TRIM commands to the underlying block
+                        device when blocks are freed.  This is useful for SSD
+                        devices and sparse/thinly-provisioned LUNs.
 
 NILFS2 usage
 ============
diff --git a/fs/nilfs2/dat.c b/fs/nilfs2/dat.c
index 187dd07ba86c..9d1e5de91afb 100644
--- a/fs/nilfs2/dat.c
+++ b/fs/nilfs2/dat.c
@@ -388,8 +388,7 @@ int nilfs_dat_translate(struct inode *dat, __u64 vblocknr, sector_t *blocknrp)
                 ret = -ENOENT;
                 goto out;
         }
-        if (blocknrp != NULL)
-                *blocknrp = blocknr;
+        *blocknrp = blocknr;
 
  out:
         kunmap_atomic(kaddr, KM_USER0);
diff --git a/fs/nilfs2/ioctl.c b/fs/nilfs2/ioctl.c
index d6b2b83de363..313d0a21da48 100644
--- a/fs/nilfs2/ioctl.c
+++ b/fs/nilfs2/ioctl.c
@@ -26,6 +26,7 @@
 #include <linux/capability.h>   /* capable() */
 #include <linux/uaccess.h>      /* copy_from_user(), copy_to_user() */
 #include <linux/vmalloc.h>
+#include <linux/mount.h>        /* mnt_want_write(), mnt_drop_write() */
 #include <linux/nilfs2_fs.h>
 #include "nilfs.h"
 #include "segment.h"
@@ -107,20 +108,28 @@ static int nilfs_ioctl_change_cpmode(struct inode *inode, struct file *filp,
 
         if (!capable(CAP_SYS_ADMIN))
                 return -EPERM;
+
+        ret = mnt_want_write(filp->f_path.mnt);
+        if (ret)
+                return ret;
+
+        ret = -EFAULT;
         if (copy_from_user(&cpmode, argp, sizeof(cpmode)))
-                return -EFAULT;
+                goto out;
 
         mutex_lock(&nilfs->ns_mount_mutex);
+
         nilfs_transaction_begin(inode->i_sb, &ti, 0);
         ret = nilfs_cpfile_change_cpmode(
                 cpfile, cpmode.cm_cno, cpmode.cm_mode);
-        if (unlikely(ret < 0)) {
+        if (unlikely(ret < 0))
                 nilfs_transaction_abort(inode->i_sb);
-                mutex_unlock(&nilfs->ns_mount_mutex);
-                return ret;
-        }
-        nilfs_transaction_commit(inode->i_sb); /* never fails */
+        else
+                nilfs_transaction_commit(inode->i_sb); /* never fails */
+
         mutex_unlock(&nilfs->ns_mount_mutex);
+out:
+        mnt_drop_write(filp->f_path.mnt);
         return ret;
 }
 
@@ -135,16 +144,23 @@ nilfs_ioctl_delete_checkpoint(struct inode *inode, struct file *filp,
 
         if (!capable(CAP_SYS_ADMIN))
                 return -EPERM;
+
+        ret = mnt_want_write(filp->f_path.mnt);
+        if (ret)
+                return ret;
+
+        ret = -EFAULT;
         if (copy_from_user(&cno, argp, sizeof(cno)))
-                return -EFAULT;
+                goto out;
 
         nilfs_transaction_begin(inode->i_sb, &ti, 0);
         ret = nilfs_cpfile_delete_checkpoint(cpfile, cno);
-        if (unlikely(ret < 0)) {
+        if (unlikely(ret < 0))
                 nilfs_transaction_abort(inode->i_sb);
-                return ret;
-        }
-        nilfs_transaction_commit(inode->i_sb); /* never fails */
+        else
+                nilfs_transaction_commit(inode->i_sb); /* never fails */
+out:
+        mnt_drop_write(filp->f_path.mnt);
         return ret;
 }
 
@@ -496,12 +512,19 @@ static int nilfs_ioctl_clean_segments(struct inode *inode, struct file *filp,
         if (!capable(CAP_SYS_ADMIN))
                 return -EPERM;
 
+        ret = mnt_want_write(filp->f_path.mnt);
+        if (ret)
+                return ret;
+
+        ret = -EFAULT;
         if (copy_from_user(argv, argp, sizeof(argv)))
-                return -EFAULT;
+                goto out;
 
+        ret = -EINVAL;
         nsegs = argv[4].v_nmembs;
         if (argv[4].v_size != argsz[4])
-                return -EINVAL;
+                goto out;
+
         /*
          * argv[4] points to segment numbers this ioctl cleans.  We
          * use kmalloc() for its buffer because memory used for the
@@ -509,9 +532,10 @@ static int nilfs_ioctl_clean_segments(struct inode *inode, struct file *filp,
          */
         kbufs[4] = memdup_user((void __user *)(unsigned long)argv[4].v_base,
                                nsegs * sizeof(__u64));
-        if (IS_ERR(kbufs[4]))
-                return PTR_ERR(kbufs[4]);
-
+        if (IS_ERR(kbufs[4])) {
+                ret = PTR_ERR(kbufs[4]);
+                goto out;
+        }
         nilfs = NILFS_SB(inode->i_sb)->s_nilfs;
 
         for (n = 0; n < 4; n++) {
@@ -563,10 +587,12 @@ static int nilfs_ioctl_clean_segments(struct inode *inode, struct file *filp,
                 nilfs_remove_all_gcinode(nilfs);
         clear_nilfs_gc_running(nilfs);
 
- out_free:
+out_free:
         while (--n >= 0)
                 vfree(kbufs[n]);
         kfree(kbufs[4]);
+out:
+        mnt_drop_write(filp->f_path.mnt);
         return ret;
 }
 
@@ -575,13 +601,17 @@ static int nilfs_ioctl_sync(struct inode *inode, struct file *filp,
 {
         __u64 cno;
         int ret;
+        struct the_nilfs *nilfs;
 
         ret = nilfs_construct_segment(inode->i_sb);
         if (ret < 0)
                 return ret;
 
         if (argp != NULL) {
-                cno = NILFS_SB(inode->i_sb)->s_nilfs->ns_cno - 1;
+                nilfs = NILFS_SB(inode->i_sb)->s_nilfs;
+                down_read(&nilfs->ns_segctor_sem);
+                cno = nilfs->ns_cno - 1;
+                up_read(&nilfs->ns_segctor_sem);
                 if (copy_to_user(argp, &cno, sizeof(cno)))
                         return -EFAULT;
         }
diff --git a/fs/nilfs2/recovery.c b/fs/nilfs2/recovery.c
index c9c96c7825dc..017bedc761a0 100644
--- a/fs/nilfs2/recovery.c
+++ b/fs/nilfs2/recovery.c
@@ -39,7 +39,6 @@ enum {
         NILFS_SEG_FAIL_IO,
         NILFS_SEG_FAIL_MAGIC,
         NILFS_SEG_FAIL_SEQ,
-        NILFS_SEG_FAIL_CHECKSUM_SEGSUM,
         NILFS_SEG_FAIL_CHECKSUM_SUPER_ROOT,
         NILFS_SEG_FAIL_CHECKSUM_FULL,
         NILFS_SEG_FAIL_CONSISTENCY,
@@ -71,10 +70,6 @@ static int nilfs_warn_segment_error(int err)
                 printk(KERN_WARNING
                        "NILFS warning: Sequence number mismatch\n");
                 break;
-        case NILFS_SEG_FAIL_CHECKSUM_SEGSUM:
-                printk(KERN_WARNING
-                       "NILFS warning: Checksum error in segment summary\n");
-                break;
         case NILFS_SEG_FAIL_CHECKSUM_SUPER_ROOT:
                 printk(KERN_WARNING
                        "NILFS warning: Checksum error in super root\n");
@@ -206,19 +201,15 @@ int nilfs_read_super_root_block(struct super_block *sb, sector_t sr_block,
  * @pseg_start: start disk block number of partial segment
  * @seg_seq: sequence number requested
  * @ssi: pointer to nilfs_segsum_info struct to store information
- * @full_check: full check flag
- *              (0: only checks segment summary CRC, 1: data CRC)
  */
 static int
 load_segment_summary(struct nilfs_sb_info *sbi, sector_t pseg_start,
-                     u64 seg_seq, struct nilfs_segsum_info *ssi,
-                     int full_check)
+                     u64 seg_seq, struct nilfs_segsum_info *ssi)
 {
         struct buffer_head *bh_sum;
         struct nilfs_segment_summary *sum;
-        unsigned long offset, nblock;
-        u64 check_bytes;
-        u32 crc, crc_sum;
+        unsigned long nblock;
+        u32 crc;
         int ret = NILFS_SEG_FAIL_IO;
 
         bh_sum = sb_bread(sbi->s_super, pseg_start);
@@ -237,34 +228,24 @@ load_segment_summary(struct nilfs_sb_info *sbi, sector_t pseg_start,
                 ret = NILFS_SEG_FAIL_SEQ;
                 goto failed;
         }
-        if (full_check) {
-                offset = sizeof(sum->ss_datasum);
-                check_bytes =
-                        ((u64)ssi->nblocks << sbi->s_super->s_blocksize_bits);
-                nblock = ssi->nblocks;
-                crc_sum = le32_to_cpu(sum->ss_datasum);
-                ret = NILFS_SEG_FAIL_CHECKSUM_FULL;
-        } else { /* only checks segment summary */
-                offset = sizeof(sum->ss_datasum) + sizeof(sum->ss_sumsum);
-                check_bytes = ssi->sumbytes;
-                nblock = ssi->nsumblk;
-                crc_sum = le32_to_cpu(sum->ss_sumsum);
-                ret = NILFS_SEG_FAIL_CHECKSUM_SEGSUM;
-        }
 
+        nblock = ssi->nblocks;
         if (unlikely(nblock == 0 ||
                      nblock > sbi->s_nilfs->ns_blocks_per_segment)) {
                 /* This limits the number of blocks read in the CRC check */
                 ret = NILFS_SEG_FAIL_CONSISTENCY;
                 goto failed;
         }
-        if (calc_crc_cont(sbi, bh_sum, &crc, offset, check_bytes,
+        if (calc_crc_cont(sbi, bh_sum, &crc, sizeof(sum->ss_datasum),
+                          ((u64)nblock << sbi->s_super->s_blocksize_bits),
                           pseg_start, nblock)) {
                 ret = NILFS_SEG_FAIL_IO;
                 goto failed;
         }
-        if (crc == crc_sum)
+        if (crc == le32_to_cpu(sum->ss_datasum))
                 ret = 0;
+        else
+                ret = NILFS_SEG_FAIL_CHECKSUM_FULL;
  failed:
         brelse(bh_sum);
  out:
@@ -598,7 +579,7 @@ static int nilfs_do_roll_forward(struct the_nilfs *nilfs,
 
         while (segnum != ri->ri_segnum || pseg_start <= ri->ri_pseg_start) {
 
-                ret = load_segment_summary(sbi, pseg_start, seg_seq, &ssi, 1);
+                ret = load_segment_summary(sbi, pseg_start, seg_seq, &ssi);
                 if (ret) {
                         if (ret == NILFS_SEG_FAIL_IO) {
                                 err = -EIO;
@@ -821,7 +802,7 @@ int nilfs_search_super_root(struct the_nilfs *nilfs, struct nilfs_sb_info *sbi,
 
         for (;;) {
                 /* Load segment summary */
-                ret = load_segment_summary(sbi, pseg_start, seg_seq, &ssi, 1);
+                ret = load_segment_summary(sbi, pseg_start, seg_seq, &ssi);
                 if (ret) {
                         if (ret == NILFS_SEG_FAIL_IO)
                                 goto failed;
diff --git a/fs/nilfs2/segbuf.c b/fs/nilfs2/segbuf.c
index 645c78656aa0..ab56fe44e377 100644
--- a/fs/nilfs2/segbuf.c
+++ b/fs/nilfs2/segbuf.c
@@ -40,6 +40,11 @@ struct nilfs_write_info {
 };
 
 
+static int nilfs_segbuf_write(struct nilfs_segment_buffer *segbuf,
+                              struct the_nilfs *nilfs);
+static int nilfs_segbuf_wait(struct nilfs_segment_buffer *segbuf);
+
+
 static struct kmem_cache *nilfs_segbuf_cachep;
 
 static void nilfs_segbuf_init_once(void *obj)
@@ -302,6 +307,19 @@ void nilfs_truncate_logs(struct list_head *logs,
         }
 }
 
+int nilfs_write_logs(struct list_head *logs, struct the_nilfs *nilfs)
+{
+        struct nilfs_segment_buffer *segbuf;
+        int ret = 0;
+
+        list_for_each_entry(segbuf, logs, sb_list) {
+                ret = nilfs_segbuf_write(segbuf, nilfs);
+                if (ret)
+                        break;
+        }
+        return ret;
+}
+
 int nilfs_wait_on_logs(struct list_head *logs)
 {
         struct nilfs_segment_buffer *segbuf;
diff --git a/fs/nilfs2/segbuf.h b/fs/nilfs2/segbuf.h
index 6af1630fb401..94dfd3517bc0 100644
--- a/fs/nilfs2/segbuf.h
+++ b/fs/nilfs2/segbuf.h
@@ -166,13 +166,10 @@ nilfs_segbuf_add_file_buffer(struct nilfs_segment_buffer *segbuf,
         segbuf->sb_sum.nfileblk++;
 }
 
-int nilfs_segbuf_write(struct nilfs_segment_buffer *segbuf,
-                       struct the_nilfs *nilfs);
-int nilfs_segbuf_wait(struct nilfs_segment_buffer *segbuf);
-
 void nilfs_clear_logs(struct list_head *logs);
 void nilfs_truncate_logs(struct list_head *logs,
                          struct nilfs_segment_buffer *last);
+int nilfs_write_logs(struct list_head *logs, struct the_nilfs *nilfs);
 int nilfs_wait_on_logs(struct list_head *logs);
 
 static inline void nilfs_destroy_logs(struct list_head *logs)
diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
index 105b508b47a8..ada2f1b947a3 100644
--- a/fs/nilfs2/segment.c
+++ b/fs/nilfs2/segment.c
@@ -1764,14 +1764,9 @@ static int nilfs_segctor_prepare_write(struct nilfs_sc_info *sci,
 static int nilfs_segctor_write(struct nilfs_sc_info *sci,
                                struct the_nilfs *nilfs)
 {
-        struct nilfs_segment_buffer *segbuf;
-        int ret = 0;
+        int ret;
 
-        list_for_each_entry(segbuf, &sci->sc_segbufs, sb_list) {
-                ret = nilfs_segbuf_write(segbuf, nilfs);
-                if (ret)
-                        break;
-        }
+        ret = nilfs_write_logs(&sci->sc_segbufs, nilfs);
         list_splice_tail_init(&sci->sc_segbufs, &sci->sc_write_logs);
         return ret;
 }
@@ -1937,8 +1932,7 @@ static void nilfs_segctor_complete_write(struct nilfs_sc_info *sci)
 {
         struct nilfs_segment_buffer *segbuf;
         struct page *bd_page = NULL, *fs_page = NULL;
-        struct nilfs_sb_info *sbi = sci->sc_sbi;
-        struct the_nilfs *nilfs = sbi->s_nilfs;
+        struct the_nilfs *nilfs = sci->sc_sbi->s_nilfs;
         int update_sr = (sci->sc_super_root != NULL);
 
         list_for_each_entry(segbuf, &sci->sc_write_logs, sb_list) {
@@ -2020,7 +2014,7 @@ static void nilfs_segctor_complete_write(struct nilfs_sc_info *sci)
         if (update_sr) {
                 nilfs_set_last_segment(nilfs, segbuf->sb_pseg_start,
                                        segbuf->sb_sum.seg_seq, nilfs->ns_cno++);
-                sbi->s_super->s_dirt = 1;
+                set_nilfs_sb_dirty(nilfs);
 
                 clear_bit(NILFS_SC_HAVE_DELTA, &sci->sc_flags);
                 clear_bit(NILFS_SC_DIRTY, &sci->sc_flags);
@@ -2425,43 +2419,43 @@ int nilfs_construct_dsync_segment(struct super_block *sb, struct inode *inode,
         return err;
 }
 
-struct nilfs_segctor_req {
-        int mode;
-        __u32 seq_accepted;
-        int sc_err;  /* construction failure */
-        int sb_err;  /* super block writeback failure */
-};
-
 #define FLUSH_FILE_BIT  (0x1) /* data file only */
 #define FLUSH_DAT_BIT   (1 << NILFS_DAT_INO) /* DAT only */
 
-static void nilfs_segctor_accept(struct nilfs_sc_info *sci,
-                                 struct nilfs_segctor_req *req)
+/**
+ * nilfs_segctor_accept - record accepted sequence count of log-write requests
+ * @sci: segment constructor object
+ */
+static void nilfs_segctor_accept(struct nilfs_sc_info *sci)
 {
-        req->sc_err = req->sb_err = 0;
         spin_lock(&sci->sc_state_lock);
-        req->seq_accepted = sci->sc_seq_request;
+        sci->sc_seq_accepted = sci->sc_seq_request;
         spin_unlock(&sci->sc_state_lock);
 
         if (sci->sc_timer)
                 del_timer_sync(sci->sc_timer);
 }
 
-static void nilfs_segctor_notify(struct nilfs_sc_info *sci,
-                                 struct nilfs_segctor_req *req)
+/**
+ * nilfs_segctor_notify - notify the result of request to caller threads
+ * @sci: segment constructor object
+ * @mode: mode of log forming
+ * @err: error code to be notified
+ */
+static void nilfs_segctor_notify(struct nilfs_sc_info *sci, int mode, int err)
 {
         /* Clear requests (even when the construction failed) */
         spin_lock(&sci->sc_state_lock);
 
-        if (req->mode == SC_LSEG_SR) {
+        if (mode == SC_LSEG_SR) {
                 sci->sc_state &= ~NILFS_SEGCTOR_COMMIT;
-                sci->sc_seq_done = req->seq_accepted;
-                nilfs_segctor_wakeup(sci, req->sc_err ? : req->sb_err);
+                sci->sc_seq_done = sci->sc_seq_accepted;
+                nilfs_segctor_wakeup(sci, err);
                 sci->sc_flush_request = 0;
         } else {
-                if (req->mode == SC_FLUSH_FILE)
+                if (mode == SC_FLUSH_FILE)
                         sci->sc_flush_request &= ~FLUSH_FILE_BIT;
-                else if (req->mode == SC_FLUSH_DAT)
+                else if (mode == SC_FLUSH_DAT)
                         sci->sc_flush_request &= ~FLUSH_DAT_BIT;
 
                 /* re-enable timer if checkpoint creation was not done */
@@ -2472,30 +2466,37 @@ static void nilfs_segctor_notify(struct nilfs_sc_info *sci,
         spin_unlock(&sci->sc_state_lock);
 }
 
-static int nilfs_segctor_construct(struct nilfs_sc_info *sci,
-                                   struct nilfs_segctor_req *req)
+/**
+ * nilfs_segctor_construct - form logs and write them to disk
+ * @sci: segment constructor object
+ * @mode: mode of log forming
+ */
+static int nilfs_segctor_construct(struct nilfs_sc_info *sci, int mode)
 {
         struct nilfs_sb_info *sbi = sci->sc_sbi;
         struct the_nilfs *nilfs = sbi->s_nilfs;
         int err = 0;
 
+        nilfs_segctor_accept(sci);
+
         if (nilfs_discontinued(nilfs))
-                req->mode = SC_LSEG_SR;
-        if (!nilfs_segctor_confirm(sci)) {
-                err = nilfs_segctor_do_construct(sci, req->mode);
-                req->sc_err = err;
-        }
+                mode = SC_LSEG_SR;
+        if (!nilfs_segctor_confirm(sci))
+                err = nilfs_segctor_do_construct(sci, mode);
+
         if (likely(!err)) {
-                if (req->mode != SC_FLUSH_DAT)
+                if (mode != SC_FLUSH_DAT)
                         atomic_set(&nilfs->ns_ndirtyblks, 0);
                 if (test_bit(NILFS_SC_SUPER_ROOT, &sci->sc_flags) &&
                     nilfs_discontinued(nilfs)) {
                         down_write(&nilfs->ns_sem);
-                        req->sb_err = nilfs_commit_super(sbi,
-                                        nilfs_altsb_need_update(nilfs));
+                        err = nilfs_commit_super(
+                                sbi, nilfs_altsb_need_update(nilfs));
                         up_write(&nilfs->ns_sem);
                 }
         }
+
+        nilfs_segctor_notify(sci, mode, err);
         return err;
 }
 
@@ -2526,7 +2527,6 @@ int nilfs_clean_segments(struct super_block *sb, struct nilfs_argv *argv,
         struct nilfs_sc_info *sci = NILFS_SC(sbi);
         struct the_nilfs *nilfs = sbi->s_nilfs;
         struct nilfs_transaction_info ti;
-        struct nilfs_segctor_req req = { .mode = SC_LSEG_SR };
         int err;
 
         if (unlikely(!sci))
@@ -2547,10 +2547,8 @@ int nilfs_clean_segments(struct super_block *sb, struct nilfs_argv *argv,
         list_splice_tail_init(&nilfs->ns_gc_inodes, &sci->sc_gc_inodes);
 
         for (;;) {
-                nilfs_segctor_accept(sci, &req);
-                err = nilfs_segctor_construct(sci, &req);
+                err = nilfs_segctor_construct(sci, SC_LSEG_SR);
                 nilfs_remove_written_gcinodes(nilfs, &sci->sc_gc_inodes);
-                nilfs_segctor_notify(sci, &req);
 
                 if (likely(!err))
                         break;
@@ -2560,6 +2558,16 @@ int nilfs_clean_segments(struct super_block *sb, struct nilfs_argv *argv,
                 set_current_state(TASK_INTERRUPTIBLE);
                 schedule_timeout(sci->sc_interval);
         }
+        if (nilfs_test_opt(sbi, DISCARD)) {
+                int ret = nilfs_discard_segments(nilfs, sci->sc_freesegs,
+                                                 sci->sc_nfreesegs);
+                if (ret) {
+                        printk(KERN_WARNING
+                               "NILFS warning: error %d on discard request, "
+                               "turning discards off for the device\n", ret);
+                        nilfs_clear_opt(sbi, DISCARD);
+                }
+        }
 
  out_unlock:
         sci->sc_freesegs = NULL;
@@ -2573,13 +2581,9 @@ static void nilfs_segctor_thread_construct(struct nilfs_sc_info *sci, int mode)
 {
         struct nilfs_sb_info *sbi = sci->sc_sbi;
         struct nilfs_transaction_info ti;
-        struct nilfs_segctor_req req = { .mode = mode };
 
         nilfs_transaction_lock(sbi, &ti, 0);
-
-        nilfs_segctor_accept(sci, &req);
-        nilfs_segctor_construct(sci, &req);
-        nilfs_segctor_notify(sci, &req);
+        nilfs_segctor_construct(sci, mode);
 
         /*
          * Unclosed segment should be retried.  We do this using sc_timer.
@@ -2635,6 +2639,7 @@ static int nilfs_segctor_flush_mode(struct nilfs_sc_info *sci)
 static int nilfs_segctor_thread(void *arg)
 {
         struct nilfs_sc_info *sci = (struct nilfs_sc_info *)arg;
+        struct the_nilfs *nilfs = sci->sc_sbi->s_nilfs;
         struct timer_list timer;
         int timeout = 0;
 
@@ -2680,7 +2685,6 @@ static int nilfs_segctor_thread(void *arg)
         } else {
                 DEFINE_WAIT(wait);
                 int should_sleep = 1;
-                struct the_nilfs *nilfs;
 
                 prepare_to_wait(&sci->sc_wait_daemon, &wait,
                                 TASK_INTERRUPTIBLE);
@@ -2701,8 +2705,8 @@ static int nilfs_segctor_thread(void *arg)
                 finish_wait(&sci->sc_wait_daemon, &wait);
                 timeout = ((sci->sc_state & NILFS_SEGCTOR_COMMIT) &&
                            time_after_eq(jiffies, sci->sc_timer->expires));
-                nilfs = sci->sc_sbi->s_nilfs;
-                if (sci->sc_super->s_dirt && nilfs_sb_need_update(nilfs))
+
+                if (nilfs_sb_dirty(nilfs) && nilfs_sb_need_update(nilfs))
                         set_nilfs_discontinued(nilfs);
         }
         goto loop;
@@ -2797,12 +2801,9 @@ static void nilfs_segctor_write_out(struct nilfs_sc_info *sci)
         do {
                 struct nilfs_sb_info *sbi = sci->sc_sbi;
                 struct nilfs_transaction_info ti;
-                struct nilfs_segctor_req req = { .mode = SC_LSEG_SR };
 
                 nilfs_transaction_lock(sbi, &ti, 0);
-                nilfs_segctor_accept(sci, &req);
-                ret = nilfs_segctor_construct(sci, &req);
-                nilfs_segctor_notify(sci, &req);
+                ret = nilfs_segctor_construct(sci, SC_LSEG_SR);
                 nilfs_transaction_unlock(sbi);
 
         } while (ret && retrycount-- > 0);
@@ -2865,8 +2866,15 @@ int nilfs_attach_segment_constructor(struct nilfs_sb_info *sbi)
         struct the_nilfs *nilfs = sbi->s_nilfs;
         int err;
 
-        /* Each field of nilfs_segctor is cleared through the initialization
-           of super-block info */
+        if (NILFS_SC(sbi)) {
+                /*
+                 * This happens if the filesystem was remounted
+                 * read/write after nilfs_error degenerated it into a
+                 * read-only mount.
+                 */
+                nilfs_detach_segment_constructor(sbi);
+        }
+
         sbi->s_sc_info = nilfs_segctor_new(sbi);
         if (!sbi->s_sc_info)
                 return -ENOMEM;
diff --git a/fs/nilfs2/segment.h b/fs/nilfs2/segment.h
index 3d3ab2f9864c..3155e0c7f415 100644
--- a/fs/nilfs2/segment.h
+++ b/fs/nilfs2/segment.h
@@ -116,6 +116,7 @@ struct nilfs_segsum_pointer {
  * @sc_wait_daemon: Daemon wait queue
  * @sc_wait_task: Start/end wait queue to control segctord task
  * @sc_seq_request: Request counter
+ * @sc_seq_accept: Accepted request count
  * @sc_seq_done: Completion counter
  * @sc_sync: Request of explicit sync operation
  * @sc_interval: Timeout value of background construction
@@ -169,6 +170,7 @@ struct nilfs_sc_info {
         wait_queue_head_t       sc_wait_task;
 
         __u32                   sc_seq_request;
+        __u32                   sc_seq_accepted;
         __u32                   sc_seq_done;
 
         int                     sc_sync;
diff --git a/fs/nilfs2/super.c b/fs/nilfs2/super.c
index 8173faee31e6..92579cc4c935 100644
--- a/fs/nilfs2/super.c
+++ b/fs/nilfs2/super.c
@@ -96,9 +96,6 @@ void nilfs_error(struct super_block *sb, const char *function,
         if (!(sb->s_flags & MS_RDONLY)) {
                 struct the_nilfs *nilfs = sbi->s_nilfs;
 
-                if (!nilfs_test_opt(sbi, ERRORS_CONT))
-                        nilfs_detach_segment_constructor(sbi);
-
                 down_write(&nilfs->ns_sem);
                 if (!(nilfs->ns_mount_state & NILFS_ERROR_FS)) {
                         nilfs->ns_mount_state |= NILFS_ERROR_FS;
@@ -301,7 +298,7 @@ int nilfs_commit_super(struct nilfs_sb_info *sbi, int dupsb)
                 memcpy(sbp[1], sbp[0], nilfs->ns_sbsize);
                 nilfs->ns_sbwtime[1] = t;
         }
-        sbi->s_super->s_dirt = 0;
+        clear_nilfs_sb_dirty(nilfs);
         return nilfs_sync_super(sbi, dupsb);
 }
 
@@ -345,7 +342,7 @@ static int nilfs_sync_fs(struct super_block *sb, int wait)
                 err = nilfs_construct_segment(sb);
 
         down_write(&nilfs->ns_sem);
-        if (sb->s_dirt)
+        if (nilfs_sb_dirty(nilfs))
                 nilfs_commit_super(sbi, 1);
         up_write(&nilfs->ns_sem);
 
@@ -481,6 +478,8 @@ static int nilfs_show_options(struct seq_file *seq, struct vfsmount *vfs)
                 seq_printf(seq, ",order=strict");
         if (nilfs_test_opt(sbi, NORECOVERY))
                 seq_printf(seq, ",norecovery");
+        if (nilfs_test_opt(sbi, DISCARD))
+                seq_printf(seq, ",discard");
 
         return 0;
 }
@@ -550,7 +549,7 @@ static const struct export_operations nilfs_export_ops = {
 enum {
         Opt_err_cont, Opt_err_panic, Opt_err_ro,
         Opt_nobarrier, Opt_snapshot, Opt_order, Opt_norecovery,
-        Opt_err,
+        Opt_discard, Opt_err,
 };
 
 static match_table_t tokens = {
@@ -561,6 +560,7 @@ static match_table_t tokens = {
         {Opt_snapshot, "cp=%u"},
         {Opt_order, "order=%s"},
         {Opt_norecovery, "norecovery"},
+        {Opt_discard, "discard"},
         {Opt_err, NULL}
 };
 
@@ -614,6 +614,9 @@ static int parse_options(char *options, struct super_block *sb)
                 case Opt_norecovery:
                         nilfs_set_opt(sbi, NORECOVERY);
                         break;
+                case Opt_discard:
+                        nilfs_set_opt(sbi, DISCARD);
+                        break;
                 default:
                         printk(KERN_ERR
                                "NILFS: Unrecognized mount option \"%s\"\n", p);
diff --git a/fs/nilfs2/the_nilfs.c b/fs/nilfs2/the_nilfs.c
index 6241e1722efc..92733d5651d2 100644
--- a/fs/nilfs2/the_nilfs.c
+++ b/fs/nilfs2/the_nilfs.c
@@ -646,6 +646,44 @@ int init_nilfs(struct the_nilfs *nilfs, struct nilfs_sb_info *sbi, char *data)
         goto out;
 }
 
+int nilfs_discard_segments(struct the_nilfs *nilfs, __u64 *segnump,
+                            size_t nsegs)
+{
+        sector_t seg_start, seg_end;
+        sector_t start = 0, nblocks = 0;
+        unsigned int sects_per_block;
+        __u64 *sn;
+        int ret = 0;
+
+        sects_per_block = (1 << nilfs->ns_blocksize_bits) /
+                bdev_logical_block_size(nilfs->ns_bdev);
+        for (sn = segnump; sn < segnump + nsegs; sn++) {
+                nilfs_get_segment_range(nilfs, *sn, &seg_start, &seg_end);
+
+                if (!nblocks) {
+                        start = seg_start;
+                        nblocks = seg_end - seg_start + 1;
+                } else if (start + nblocks == seg_start) {
+                        nblocks += seg_end - seg_start + 1;
+                } else {
+                        ret = blkdev_issue_discard(nilfs->ns_bdev,
+                                                   start * sects_per_block,
+                                                   nblocks * sects_per_block,
+                                                   GFP_NOFS,
+                                                   DISCARD_FL_BARRIER);
+                        if (ret < 0)
+                                return ret;
+                        nblocks = 0;
+                }
+        }
+        if (nblocks)
+                ret = blkdev_issue_discard(nilfs->ns_bdev,
+                                           start * sects_per_block,
+                                           nblocks * sects_per_block,
+                                           GFP_NOFS, DISCARD_FL_BARRIER);
+        return ret;
+}
+
 int nilfs_count_free_blocks(struct the_nilfs *nilfs, sector_t *nblocks)
 {
         struct inode *dat = nilfs_dat_inode(nilfs);
diff --git a/fs/nilfs2/the_nilfs.h b/fs/nilfs2/the_nilfs.h
index 589786e33464..e9795f1724d7 100644
--- a/fs/nilfs2/the_nilfs.h
+++ b/fs/nilfs2/the_nilfs.h
@@ -38,6 +38,7 @@ enum {
                                    the latest checkpoint was loaded */
         THE_NILFS_DISCONTINUED, /* 'next' pointer chain has broken */
         THE_NILFS_GC_RUNNING,   /* gc process is running */
+        THE_NILFS_SB_DIRTY,     /* super block is dirty */
 };
 
 /**
@@ -197,6 +198,7 @@ THE_NILFS_FNS(INIT, init)
 THE_NILFS_FNS(LOADED, loaded)
 THE_NILFS_FNS(DISCONTINUED, discontinued)
 THE_NILFS_FNS(GC_RUNNING, gc_running)
+THE_NILFS_FNS(SB_DIRTY, sb_dirty)
 
 /* Minimum interval of periodical update of superblocks (in seconds) */
 #define NILFS_SB_FREQ           10
@@ -221,6 +223,7 @@ struct the_nilfs *find_or_create_nilfs(struct block_device *);
 void put_nilfs(struct the_nilfs *);
 int init_nilfs(struct the_nilfs *, struct nilfs_sb_info *, char *);
 int load_nilfs(struct the_nilfs *, struct nilfs_sb_info *);
+int nilfs_discard_segments(struct the_nilfs *, __u64 *, size_t);
 int nilfs_count_free_blocks(struct the_nilfs *, sector_t *);
 struct nilfs_sb_info *nilfs_find_sbinfo(struct the_nilfs *, int, __u64);
 int nilfs_checkpoint_is_mounted(struct the_nilfs *, __u64, int);
diff --git a/include/linux/nilfs2_fs.h b/include/linux/nilfs2_fs.h
index 3fe02cf8b65a..640702e97457 100644
--- a/include/linux/nilfs2_fs.h
+++ b/include/linux/nilfs2_fs.h
@@ -153,6 +153,7 @@ struct nilfs_super_root {
                                                    semantics also for data */
 #define NILFS_MOUNT_NORECOVERY          0x4000  /* Disable write access during
                                                    mount-time recovery */
+#define NILFS_MOUNT_DISCARD             0x8000  /* Issue DISCARD requests */
 
 
 /**