linux-kernel - [PATCH v8 13/20] erofs: add erofs_fscache_read

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Date:   Wed,  6 Apr 2022 15:56:05 +0800
From:   Jeffle Xu <jefflexu@...ux.alibaba.com>
To:     dhowells@...hat.com, linux-cachefs@...hat.com, xiang@...nel.org,
        chao@...nel.org, linux-erofs@...ts.ozlabs.org
Cc:     torvalds@...ux-foundation.org, gregkh@...uxfoundation.org,
        willy@...radead.org, linux-fsdevel@...r.kernel.org,
        joseph.qi@...ux.alibaba.com, bo.liu@...ux.alibaba.com,
        tao.peng@...ux.alibaba.com, gerry@...ux.alibaba.com,
        eguan@...ux.alibaba.com, linux-kernel@...r.kernel.org,
        luodaowen.backend@...edance.com, tianzichen@...ishou.com,
        fannaihao@...du.com
Subject: [PATCH v8 13/20] erofs: add erofs_fscache_read_folios() helper

Add erofs_fscache_read_folios() helper reading from fscache. It supports
on-demand read semantics. That is, it will make the backend prepare for
the data when cache miss. Once data ready, it will reinitiate a read
from the cache.

This helper can then be used to implement .readpage()/.readahead() of
on-demand read semantics.

Signed-off-by: Jeffle Xu <jefflexu@...ux.alibaba.com>
---
 fs/erofs/fscache.c | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
index 1c88614203d2..d38a6efc8e50 100644
--- a/fs/erofs/fscache.c
+++ b/fs/erofs/fscache.c
@@ -5,6 +5,35 @@
 #include <linux/fscache.h>
 #include "internal.h"
 
+/*
+ * Read data from fscache and fill the read data into page cache described by
+ * @start/len, which shall be both aligned with PAGE_SIZE. @pstart describes
+ * the start physical address in the cache file.
+ */
+static int erofs_fscache_read_folios(struct fscache_cookie *cookie,
+				     struct address_space *mapping,
+				     loff_t start, size_t len,
+				     loff_t pstart)
+{
+	struct netfs_cache_resources cres;
+	struct iov_iter iter;
+	int ret;
+
+	memset(&cres, 0, sizeof(cres));
+
+	ret = fscache_begin_read_operation(&cres, cookie);
+	if (ret)
+		return ret;
+
+	iov_iter_xarray(&iter, READ, &mapping->i_pages, start, len);
+
+	ret = fscache_read(&cres, pstart, &iter,
+			   NETFS_READ_HOLE_ONDEMAND, NULL, NULL);
+
+	fscache_end_operation(&cres);
+	return ret;
+}
+
 static const struct address_space_operations erofs_fscache_meta_aops = {
 };
 
-- 
2.27.0