[RFC PATCH v6 7/7] erofs: implement .fadvise for page cache share

[Hongzhen Luo <hongzhen@linux.alibaba.com>]

This patch implements the .fadvise interface for page cache share.
Similar to overlayfs, it drops those clean, unused pages through
vfs_fadvise().

Signed-off-by: Hongzhen Luo <hongzhen@linux.alibaba.com>
---
 fs/erofs/ishare.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/fs/erofs/ishare.c b/fs/erofs/ishare.c
index e68bb1a6cf4b..a7c2be5d6f25 100644
--- a/fs/erofs/ishare.c
+++ b/fs/erofs/ishare.c
@@ -230,6 +230,14 @@ static int erofs_ishare_mmap(struct file *file, struct vm_area_struct *vma)
 	return 0;
 }
 
+static int erofs_ishare_fadvice(struct file *realfile, loff_t offset, loff_t len,
+				int advice)
+{
+	struct file *file = realfile->private_data;
+
+	return vfs_fadvise(file, offset, len, advice);
+}
+
 const struct file_operations erofs_ishare_fops = {
 	.open		= erofs_ishare_file_open,
 	.llseek		= generic_file_llseek,
@@ -238,6 +246,7 @@ const struct file_operations erofs_ishare_fops = {
 	.release	= erofs_ishare_file_release,
 	.get_unmapped_area = thp_get_unmapped_area,
 	.splice_read	= filemap_splice_read,
+	.fadvise	= erofs_ishare_fadvice,
 };
 
 void erofs_read_begin(struct erofs_read_ctx *rdctx)
-- 
2.43.5