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Subject[PATCH v4 13/21] erofs: add erofs_fscache_read_pages() helper
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Add erofs_fscache_read_pages() 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.

Besides also add erofs_fscache_read_page() wrapper helper.

Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
---
fs/erofs/fscache.c | 38 ++++++++++++++++++++++++++++++++++++++
1 file changed, 38 insertions(+)

diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
index 4d83125ff896..3f9f7d6ede57 100644
--- a/fs/erofs/fscache.c
+++ b/fs/erofs/fscache.c
@@ -6,6 +6,44 @@

static struct fscache_volume *volume;

+/*
+ * erofs_fscache_read_pages - Read data from fscache.
+ *
+ * Fill the readed data into page cache described by @start/len, which
+ * shall be both aligned with PAGE_SIZE. @pstart describes the corresponding
+ * physical start address in the cache file.
+ */
+static int erofs_fscache_read_pages(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 inline int erofs_fscache_read_page(struct fscache_cookie *cookie,
+ struct page *page, loff_t pstart)
+{
+ return erofs_fscache_read_pages(cookie, page_file_mapping(page),
+ page_offset(page), PAGE_SIZE, pstart);
+}
+
static const struct address_space_operations erofs_fscache_blob_aops = {
};

--
2.27.0
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