[PATCH 6/8] zonefs: Add active seq file accounting

[Damien Le Moal <damien.lemoal@opensource.wdc.com>]

Modify struct zonefs_sb_info to add the s_active_seq_files atomic to
count the number of seq files representing a zone that is partially
written or explicitly open, that is, to count sequential files with
a zone that is in an active state on the device.

The helper function zonefs_account_active() is introduced to update
this counter whenever a file is written or truncated. This helper is
also used in the zonefs_seq_file_write_open() and
zonefs_seq_file_write_close() functions when the explicit_open mount
option is used.

The s_active_seq_files counter is exported through sysfs using the
read-only attribute nr_active_seq_files. The device maximum number of
active zones is also exported through sysfs with the read-only attribute
max_active_seq_files.

Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
---
 fs/zonefs/super.c  | 62 +++++++++++++++++++++++++++++++++++++++++++---
 fs/zonefs/sysfs.c  | 14 +++++++++++
 fs/zonefs/zonefs.h |  4 +++
 3 files changed, 76 insertions(+), 4 deletions(-)

diff --git a/fs/zonefs/super.c b/fs/zonefs/super.c
index aa359f27102e..3934a68520fe 100644
--- a/fs/zonefs/super.c
+++ b/fs/zonefs/super.c
@@ -27,6 +27,37 @@
 #define CREATE_TRACE_POINTS
 #include "trace.h"
 
+/*
+ * Manage the active zone count. Called with zi->i_truncate_mutex held.
+ */
+static void zonefs_account_active(struct inode *inode)
+{
+	struct zonefs_sb_info *sbi = ZONEFS_SB(inode->i_sb);
+	struct zonefs_inode_info *zi = ZONEFS_I(inode);
+
+	if (zi->i_ztype != ZONEFS_ZTYPE_SEQ)
+		return;
+
+	/*
+	 * If the zone is active, that is, if it is explicitly open or
+	 * partially written, check if it was already accounted as active.
+	 */
+	if ((zi->i_flags & ZONEFS_ZONE_OPEN) ||
+	    (zi->i_wpoffset > 0 && zi->i_wpoffset < zi->i_max_size)) {
+		if (!(zi->i_flags & ZONEFS_ZONE_ACTIVE)) {
+			zi->i_flags |= ZONEFS_ZONE_ACTIVE;
+			atomic_inc(&sbi->s_active_seq_files);
+		}
+		return;
+	}
+
+	/* The zone is not active. If it was, update the active count */
+	if (zi->i_flags & ZONEFS_ZONE_ACTIVE) {
+		zi->i_flags &= ~ZONEFS_ZONE_ACTIVE;
+		atomic_dec(&sbi->s_active_seq_files);
+	}
+}
+
 static inline int zonefs_zone_mgmt(struct inode *inode,
 				   enum req_opf op)
 {
@@ -68,8 +99,13 @@ static inline void zonefs_i_size_write(struct inode *inode, loff_t isize)
 	 * A full zone is no longer open/active and does not need
 	 * explicit closing.
 	 */
-	if (isize >= zi->i_max_size)
-		zi->i_flags &= ~ZONEFS_ZONE_OPEN;
+	if (isize >= zi->i_max_size) {
+		struct zonefs_sb_info *sbi = ZONEFS_SB(inode->i_sb);
+
+		if (zi->i_flags & ZONEFS_ZONE_ACTIVE)
+			atomic_dec(&sbi->s_active_seq_files);
+		zi->i_flags &= ~(ZONEFS_ZONE_OPEN | ZONEFS_ZONE_ACTIVE);
+	}
 }
 
 static int zonefs_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
@@ -397,6 +433,7 @@ static int zonefs_io_error_cb(struct blk_zone *zone, unsigned int idx,
 	zonefs_update_stats(inode, data_size);
 	zonefs_i_size_write(inode, data_size);
 	zi->i_wpoffset = data_size;
+	zonefs_account_active(inode);
 
 	return 0;
 }
@@ -508,6 +545,7 @@ static int zonefs_file_truncate(struct inode *inode, loff_t isize)
 	zonefs_update_stats(inode, isize);
 	truncate_setsize(inode, isize);
 	zi->i_wpoffset = isize;
+	zonefs_account_active(inode);
 
 unlock:
 	mutex_unlock(&zi->i_truncate_mutex);
@@ -866,8 +904,15 @@ static ssize_t zonefs_file_dio_write(struct kiocb *iocb, struct iov_iter *from)
 	    (ret > 0 || ret == -EIOCBQUEUED)) {
 		if (ret > 0)
 			count = ret;
+
+		/*
+		 * Update the zone write pointer offset assuming the write
+		 * operation succeeded. If it did not, the error recovery path
+		 * will correct it. Also do active seq file accounting.
+		 */
 		mutex_lock(&zi->i_truncate_mutex);
 		zi->i_wpoffset += count;
+		zonefs_account_active(inode);
 		mutex_unlock(&zi->i_truncate_mutex);
 	}
 
@@ -1052,6 +1097,7 @@ static int zonefs_seq_file_write_open(struct inode *inode)
 					goto unlock;
 				}
 				zi->i_flags |= ZONEFS_ZONE_OPEN;
+				zonefs_account_active(inode);
 			}
 		}
 	}
@@ -1119,6 +1165,7 @@ static void zonefs_seq_file_write_close(struct inode *inode)
 		}
 
 		zi->i_flags &= ~ZONEFS_ZONE_OPEN;
+		zonefs_account_active(inode);
 	}
 
 	atomic_dec(&sbi->s_wro_seq_files);
@@ -1325,7 +1372,7 @@ static int zonefs_init_file_inode(struct inode *inode, struct blk_zone *zone,
 	struct super_block *sb = inode->i_sb;
 	struct zonefs_sb_info *sbi = ZONEFS_SB(sb);
 	struct zonefs_inode_info *zi = ZONEFS_I(inode);
-	int ret = 0;
+	int ret;
 
 	inode->i_ino = zone->start >> sbi->s_zone_sectors_shift;
 	inode->i_mode = S_IFREG | sbi->s_perm;
@@ -1363,9 +1410,13 @@ static int zonefs_init_file_inode(struct inode *inode, struct blk_zone *zone,
 		mutex_lock(&zi->i_truncate_mutex);
 		ret = zonefs_zone_mgmt(inode, REQ_OP_ZONE_CLOSE);
 		mutex_unlock(&zi->i_truncate_mutex);
+		if (ret)
+			return ret;
 	}
 
-	return ret;
+	zonefs_account_active(inode);
+
+	return 0;
 }
 
 static struct dentry *zonefs_create_inode(struct dentry *parent,
@@ -1711,6 +1762,9 @@ static int zonefs_fill_super(struct super_block *sb, void *data, int silent)
 		sbi->s_mount_opts &= ~ZONEFS_MNTOPT_EXPLICIT_OPEN;
 	}
 
+	atomic_set(&sbi->s_active_seq_files, 0);
+	sbi->s_max_active_seq_files = bdev_max_active_zones(sb->s_bdev);
+
 	ret = zonefs_read_super(sb);
 	if (ret)
 		return ret;
diff --git a/fs/zonefs/sysfs.c b/fs/zonefs/sysfs.c
index eaeaf983ed87..9cb6755ce39a 100644
--- a/fs/zonefs/sysfs.c
+++ b/fs/zonefs/sysfs.c
@@ -51,9 +51,23 @@ static ssize_t nr_wro_seq_files_show(struct zonefs_sb_info *sbi, char *buf)
 }
 ZONEFS_SYSFS_ATTR_RO(nr_wro_seq_files);
 
+static ssize_t max_active_seq_files_show(struct zonefs_sb_info *sbi, char *buf)
+{
+	return sysfs_emit(buf, "%u\n", sbi->s_max_active_seq_files);
+}
+ZONEFS_SYSFS_ATTR_RO(max_active_seq_files);
+
+static ssize_t nr_active_seq_files_show(struct zonefs_sb_info *sbi, char *buf)
+{
+	return sysfs_emit(buf, "%d\n", atomic_read(&sbi->s_active_seq_files));
+}
+ZONEFS_SYSFS_ATTR_RO(nr_active_seq_files);
+
 static struct attribute *zonefs_sysfs_attrs[] = {
 	ATTR_LIST(max_wro_seq_files),
 	ATTR_LIST(nr_wro_seq_files),
+	ATTR_LIST(max_active_seq_files),
+	ATTR_LIST(nr_active_seq_files),
 	NULL,
 };
 ATTRIBUTE_GROUPS(zonefs_sysfs);
diff --git a/fs/zonefs/zonefs.h b/fs/zonefs/zonefs.h
index 77d2d153c59d..4b3de66c3233 100644
--- a/fs/zonefs/zonefs.h
+++ b/fs/zonefs/zonefs.h
@@ -40,6 +40,7 @@ static inline enum zonefs_ztype zonefs_zone_type(struct blk_zone *zone)
 }
 
 #define ZONEFS_ZONE_OPEN	(1 << 0)
+#define ZONEFS_ZONE_ACTIVE	(1 << 1)
 
 /*
  * In-memory inode data.
@@ -186,6 +187,9 @@ struct zonefs_sb_info {
 	unsigned int		s_max_wro_seq_files;
 	atomic_t		s_wro_seq_files;
 
+	unsigned int		s_max_active_seq_files;
+	atomic_t		s_active_seq_files;
+
 	bool			s_sysfs_registered;
 	struct kobject		s_kobj;
 	struct completion	s_kobj_unregister;
-- 
2.35.1