[PATCH 4/9] nilfs2: add function to modify su_nlive_blks

[Andreas Rohner <andreas.rohner-hi6Y0CQ0nG0@public.gmane.org>]

This patch adds a function to modify the su_nlive_blks field of the
nilfs_segment_usage structure in the SUFILE. By using positive or
negative integers, it is possible to add and substract any value from
the su_nlive_blks field.

The use of a modification cache is optional and by passing a NULL
pointer the value will be added or subtracted directly. Otherwise it is
necessary to call nilfs_sufile_flush_nlive_blks() at some point to make
the modifications persistent.

The modification cache is useful, because it allows for small values,
like simple increments and decrements, to be added up before writing
them to the SUFILE.

Signed-off-by: Andreas Rohner <andreas.rohner-hi6Y0CQ0nG0@public.gmane.org>
---
 fs/nilfs2/sufile.c | 138 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 fs/nilfs2/sufile.h |   5 ++
 2 files changed, 143 insertions(+)

diff --git a/fs/nilfs2/sufile.c b/fs/nilfs2/sufile.c
index ae08050..574a77e 100644
--- a/fs/nilfs2/sufile.c
+++ b/fs/nilfs2/sufile.c
@@ -1380,6 +1380,144 @@ static inline int nilfs_sufile_mc_update(struct inode *sufile,
 }
 
 /**
+ * nilfs_sufile_do_flush_nlive_blks - apply modification to su_nlive_blks
+ * @sufile: inode of segment usage file
+ * @mod: modification structure
+ * @header_bh: sufile header block
+ * @su_bh: block containing segment usage of m_segnum in @mod
+ *
+ * Description: nilfs_sufile_do_flush_nlive_blks() is a callback function
+ * used with nilfs_sufile_updatev(), that adds m_value in @mod to
+ * the su_nlive_blks field of the segment usage entry belonging to m_segnum.
+ */
+static void nilfs_sufile_do_flush_nlive_blks(struct inode *sufile,
+					     struct nilfs_sufile_mod *mod,
+					     struct buffer_head *header_bh,
+					     struct buffer_head *su_bh)
+{
+	struct the_nilfs *nilfs = sufile->i_sb->s_fs_info;
+	struct nilfs_segment_usage *su;
+	void *kaddr;
+	__u32 nblocks, nlive_blocks;
+	__u64 segnum = mod->m_segnum;
+	__s64 value = mod->m_value;
+
+	if (!value)
+		return;
+
+	kaddr = kmap_atomic(su_bh->b_page);
+
+	su = nilfs_sufile_block_get_segment_usage(sufile, segnum, su_bh, kaddr);
+	WARN_ON(nilfs_segment_usage_error(su));
+
+	nblocks = le32_to_cpu(su->su_nblocks);
+	nlive_blocks = le32_to_cpu(su->su_nlive_blks);
+
+	value += nlive_blocks;
+	if (value < 0)
+		value = 0;
+	else if (value > nblocks)
+		value = nblocks;
+
+	/* do nothing if the value didn't change */
+	if (value != nlive_blocks) {
+		su->su_nlive_blks = cpu_to_le32(value);
+		su->su_nlive_lastmod = cpu_to_le64(nilfs->ns_ctime);
+	}
+
+	kunmap_atomic(kaddr);
+
+	if (value != nlive_blocks) {
+		mark_buffer_dirty(su_bh);
+		nilfs_mdt_mark_dirty(sufile);
+	}
+}
+
+/**
+ * nilfs_sufile_flush_nlive_blks - flush mod cache to su_nlive_blks
+ * @sufile: inode of segment usage file
+ * @mc: modification cache
+ *
+ * Description: nilfs_sufile_flush_nlive_blks() flushes the cached
+ * modifications in @mc, by applying them to the su_nlive_blks field of
+ * the corresponding segment usage entries. @mc can be NULL or empty. If
+ * the sufile extension needed to support su_nlive_blks is not supported the
+ * function will abort without error.
+ *
+ * Return Value: On success, zero is returned.  On error, one of the
+ * following negative error codes is returned.
+ *
+ * %-EIO - I/O error.
+ *
+ * %-ENOMEM - Insufficient amount of memory available.
+ *
+ * %-ENOENT - Given segment usage is in hole block
+ *
+ * %-EINVAL - Invalid segment usage number
+ */
+int nilfs_sufile_flush_nlive_blks(struct inode *sufile,
+				  struct nilfs_sufile_mod_cache *mc)
+{
+	int ret;
+
+	if (!mc || !mc->mc_size || !nilfs_sufile_ext_supported(sufile))
+		return 0;
+
+	ret = nilfs_sufile_mc_flush(sufile, mc,
+				    nilfs_sufile_do_flush_nlive_blks);
+
+	nilfs_sufile_mc_clear(mc);
+
+	return ret;
+}
+
+/**
+ * nilfs_sufile_mod_nlive_blks - modifiy su_nlive_blks using mod cache
+ * @sufile: inode of segment usage file
+ * @mc: modification cache
+ * @segnum: segment number
+ * @value: signed value (can be positive and negative)
+ *
+ * Description: nilfs_sufile_mod_nlive_blks() adds @value to the su_nlive_blks
+ * field of the segment usage entry for @segnum. If @mc is not NULL it first
+ * accumulates all modifications in the cache and flushes it if it is full.
+ * Otherwise the change is applied directly.
+ *
+ * Return Value: On success, zero is returned.  On error, one of the
+ * following negative error codes is returned.
+ *
+ * %-EIO - I/O error.
+ *
+ * %-ENOMEM - Insufficient amount of memory available.
+ *
+ * %-ENOENT - Given segment usage is in hole block
+ *
+ * %-EINVAL - Invalid segment usage number
+ */
+int nilfs_sufile_mod_nlive_blks(struct inode *sufile,
+				struct nilfs_sufile_mod_cache *mc,
+				__u64 segnum, __s64 value)
+{
+	int ret;
+
+	if (!value || !nilfs_sufile_ext_supported(sufile))
+		return 0;
+
+	if (!mc)
+		return nilfs_sufile_mc_update(sufile, segnum, value,
+				nilfs_sufile_do_flush_nlive_blks);
+
+	if (!nilfs_sufile_mc_add(mc, segnum, value))
+		return 0;
+
+	ret = nilfs_sufile_flush_nlive_blks(sufile, mc);
+
+	nilfs_sufile_mc_reset(mc, segnum, value);
+
+	return ret;
+}
+
+/**
  * nilfs_sufile_read - read or get sufile inode
  * @sb: super block instance
  * @susize: size of a segment usage entry
diff --git a/fs/nilfs2/sufile.h b/fs/nilfs2/sufile.h
index d56498b..ae3c52a 100644
--- a/fs/nilfs2/sufile.h
+++ b/fs/nilfs2/sufile.h
@@ -195,4 +195,9 @@ static inline void nilfs_sufile_mc_destroy(struct nilfs_sufile_mod_cache *mc)
 	}
 }
 
+int nilfs_sufile_flush_nlive_blks(struct inode *,
+				  struct nilfs_sufile_mod_cache *);
+int nilfs_sufile_mod_nlive_blks(struct inode *, struct nilfs_sufile_mod_cache *,
+				__u64, __s64);
+
 #endif	/* _NILFS_SUFILE_H */
-- 
2.3.0

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