[RFC v2 4/4] shmem: Add support for generic FS events

[Beata Michalska <b.michalska@xxxxxxxxxxx>]

Add support for the generic FS events interface
covering threshold notifiactions and the ENOSPC
warning.

Signed-off-by: Beata Michalska <b.michalska@xxxxxxxxxxx>
---
 mm/shmem.c |   33 ++++++++++++++++++++++++++++++---
 1 file changed, 30 insertions(+), 3 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index cf2d0ca..a044d12 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -201,6 +201,7 @@ static int shmem_reserve_inode(struct super_block *sb)
 		spin_lock(&sbinfo->stat_lock);
 		if (!sbinfo->free_inodes) {
 			spin_unlock(&sbinfo->stat_lock);
+			fs_event_notify(sb, FS_WARN_ENOSPC);
 			return -ENOSPC;
 		}
 		sbinfo->free_inodes--;
@@ -239,8 +240,10 @@ static void shmem_recalc_inode(struct inode *inode)
 	freed = info->alloced - info->swapped - inode->i_mapping->nrpages;
 	if (freed > 0) {
 		struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
-		if (sbinfo->max_blocks)
+		if (sbinfo->max_blocks) {
 			percpu_counter_add(&sbinfo->used_blocks, -freed);
+			fs_event_free_space(inode->i_sb, freed);
+		}
 		info->alloced -= freed;
 		inode->i_blocks -= freed * BLOCKS_PER_PAGE;
 		shmem_unacct_blocks(info->flags, freed);
@@ -1164,6 +1167,7 @@ repeat:
 				goto unacct;
 			}
 			percpu_counter_inc(&sbinfo->used_blocks);
+			fs_event_alloc_space(inode->i_sb, 1);
 		}
 
 		page = shmem_alloc_page(gfp, info, index);
@@ -1245,8 +1249,10 @@ trunc:
 	spin_unlock(&info->lock);
 decused:
 	sbinfo = SHMEM_SB(inode->i_sb);
-	if (sbinfo->max_blocks)
+	if (sbinfo->max_blocks) {
 		percpu_counter_add(&sbinfo->used_blocks, -1);
+		fs_event_free_space(inode->i_sb, 1);
+	}
 unacct:
 	shmem_unacct_blocks(info->flags, 1);
 failed:
@@ -1258,12 +1264,16 @@ unlock:
 		unlock_page(page);
 		page_cache_release(page);
 	}
-	if (error == -ENOSPC && !once++) {
+	if (error == -ENOSPC) {
+		if (!once++) {
 		info = SHMEM_I(inode);
 		spin_lock(&info->lock);
 		shmem_recalc_inode(inode);
 		spin_unlock(&info->lock);
 		goto repeat;
+		} else {
+			fs_event_notify(inode->i_sb, FS_WARN_ENOSPC);
+		}
 	}
 	if (error == -EEXIST)	/* from above or from radix_tree_insert */
 		goto repeat;
@@ -2729,12 +2739,26 @@ static int shmem_encode_fh(struct inode *inode, __u32 *fh, int *len,
 	return 1;
 }
 
+static void shmem_trace_query(struct super_block *sb, u64 *ncount)
+{
+	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
+
+	if (sbinfo->max_blocks)
+		*ncount = sbinfo->max_blocks -
+			percpu_counter_sum(&sbinfo->used_blocks);
+
+}
+
 static const struct export_operations shmem_export_ops = {
 	.get_parent     = shmem_get_parent,
 	.encode_fh      = shmem_encode_fh,
 	.fh_to_dentry	= shmem_fh_to_dentry,
 };
 
+static const struct fs_trace_operations shmem_trace_ops = {
+	.query	= shmem_trace_query,
+};
+
 static int shmem_parse_options(char *options, struct shmem_sb_info *sbinfo,
 			       bool remount)
 {
@@ -3020,6 +3044,9 @@ int shmem_fill_super(struct super_block *sb, void *data, int silent)
 		sb->s_flags |= MS_NOUSER;
 	}
 	sb->s_export_op = &shmem_export_ops;
+	sb->s_etrace.ops = &shmem_trace_ops;
+	sb->s_etrace.events_cap_mask = FS_EVENTS_ALL;
+
 	sb->s_flags |= MS_NOSEC;
 #else
 	sb->s_flags |= MS_NOUSER;
-- 
1.7.9.5

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