nilfs2: add ioctl which limits range of segment to be allocated

This adds a new ioctl command which limits range of segment to be
allocated.  This is intended to gather data whithin a range of the
partition before shrinking the filesystem, or to control new log
location for some purpose.

If a range is specified by the ioctl, segment allocator of nilfs tries
to allocate new segments from the range unless no free segments are
available there.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

1 files changed, 63 insertions, 10 deletions

diff --git a/fs/nilfs2/sufile.c b/fs/nilfs2/sufile.c
index 1d6f488ccae8..f4374df00ad5 100644
--- a/fs/nilfs2/sufile.c
+++ b/fs/nilfs2/sufile.c
@@ -33,7 +33,9 @@
 
 struct nilfs_sufile_info {
         struct nilfs_mdt_info mi;
-        unsigned long ncleansegs;
+        unsigned long ncleansegs;/* number of clean segments */
+        __u64 allocmin;         /* lower limit of allocatable segment range */
+        __u64 allocmax;         /* upper limit of allocatable segment range */
 };
 
 static inline struct nilfs_sufile_info *NILFS_SUI(struct inode *sufile)
@@ -248,6 +250,35 @@ int nilfs_sufile_update(struct inode *sufile, __u64 segnum, int create,
 }
 
 /**
+ * nilfs_sufile_set_alloc_range - limit range of segment to be allocated
+ * @sufile: inode of segment usage file
+ * @start: minimum segment number of allocatable region (inclusive)
+ * @end: maximum segment number of allocatable region (inclusive)
+ *
+ * Return Value: On success, 0 is returned.  On error, one of the
+ * following negative error codes is returned.
+ *
+ * %-ERANGE - invalid segment region
+ */
+int nilfs_sufile_set_alloc_range(struct inode *sufile, __u64 start, __u64 end)
+{
+        struct nilfs_sufile_info *sui = NILFS_SUI(sufile);
+        __u64 nsegs;
+        int ret = -ERANGE;
+
+        down_write(&NILFS_MDT(sufile)->mi_sem);
+        nsegs = nilfs_sufile_get_nsegments(sufile);
+
+        if (start <= end && end < nsegs) {
+                sui->allocmin = start;
+                sui->allocmax = end;
+                ret = 0;
+        }
+        up_write(&NILFS_MDT(sufile)->mi_sem);
+        return ret;
+}
+
+/**
  * nilfs_sufile_alloc - allocate a segment
  * @sufile: inode of segment usage file
  * @segnump: pointer to segment number
@@ -269,11 +300,12 @@ int nilfs_sufile_alloc(struct inode *sufile, __u64 *segnump)
         struct buffer_head *header_bh, *su_bh;
         struct nilfs_sufile_header *header;
         struct nilfs_segment_usage *su;
+        struct nilfs_sufile_info *sui = NILFS_SUI(sufile);
         size_t susz = NILFS_MDT(sufile)->mi_entry_size;
         __u64 segnum, maxsegnum, last_alloc;
         void *kaddr;
-        unsigned long nsegments, ncleansegs, nsus;
-        int ret, i, j;
+        unsigned long nsegments, ncleansegs, nsus, cnt;
+        int ret, j;
 
         down_write(&NILFS_MDT(sufile)->mi_sem);
 
@@ -287,13 +319,31 @@ int nilfs_sufile_alloc(struct inode *sufile, __u64 *segnump)
         kunmap_atomic(kaddr, KM_USER0);
 
         nsegments = nilfs_sufile_get_nsegments(sufile);
+        maxsegnum = sui->allocmax;
         segnum = last_alloc + 1;
-        maxsegnum = nsegments - 1;
-        for (i = 0; i < nsegments; i += nsus) {
-                if (segnum >= nsegments) {
-                        /* wrap around */
-                        segnum = 0;
-                        maxsegnum = last_alloc;
+        if (segnum < sui->allocmin || segnum > sui->allocmax)
+                segnum = sui->allocmin;
+
+        for (cnt = 0; cnt < nsegments; cnt += nsus) {
+                if (segnum > maxsegnum) {
+                        if (cnt < sui->allocmax - sui->allocmin + 1) {
+                                /*
+                                 * wrap around in the limited region.
+                                 * if allocation started from
+                                 * sui->allocmin, this never happens.
+                                 */
+                                segnum = sui->allocmin;
+                                maxsegnum = last_alloc;
+                        } else if (segnum > sui->allocmin &&
+                                   sui->allocmax + 1 < nsegments) {
+                                segnum = sui->allocmax + 1;
+                                maxsegnum = nsegments - 1;
+                        } else if (sui->allocmin > 0)  {
+                                segnum = 0;
+                                maxsegnum = sui->allocmin - 1;
+                        } else {
+                                break; /* never happens */
+                        }
                 }
                 ret = nilfs_sufile_get_segment_usage_block(sufile, segnum, 1,
                                                            &su_bh);
@@ -319,7 +369,7 @@ int nilfs_sufile_alloc(struct inode *sufile, __u64 *segnump)
                         header->sh_last_alloc = cpu_to_le64(segnum);
                         kunmap_atomic(kaddr, KM_USER0);
 
-                        NILFS_SUI(sufile)->ncleansegs--;
+                        sui->ncleansegs--;
                         nilfs_mdt_mark_buffer_dirty(header_bh);
                         nilfs_mdt_mark_buffer_dirty(su_bh);
                         nilfs_mdt_mark_dirty(sufile);
@@ -679,6 +729,9 @@ int nilfs_sufile_read(struct super_block *sb, size_t susize,
         kunmap_atomic(kaddr, KM_USER0);
         brelse(header_bh);
 
+        sui->allocmax = nilfs_sufile_get_nsegments(sufile) - 1;
+        sui->allocmin = 0;
+
         unlock_new_inode(sufile);
  out:
         *inodep = sufile;