[PATCH v6 14/22] erofs: add erofs_fscache_read_folios() helper

Jeffle Xu
2022-03-25T12:23:30Z

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.

Besides also add erofs_fscache_read_folio() wrapper helper.

Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
---
fs/erofs/fscache.c | 39 +++++++++++++++++++++++++++++++++++++++
1 file changed, 39 insertions(+)

diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
index 30383d9adb62..6a55f7b5f883 100644
--- a/fs/erofs/fscache.c
+++ b/fs/erofs/fscache.c
@@ -7,6 +7,45 @@

static struct fscache_volume *volume;

+/*
+ * erofs_fscache_read_folios - Read data from fscache.
+ *
+ * Fill the read 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_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 inline int erofs_fscache_read_folio(struct fscache_cookie *cookie,
+ struct folio *folio, loff_t pstart)
+{
+ return erofs_fscache_read_folios(cookie, folio_file_mapping(folio),
+ folio_pos(folio), folio_size(folio),
+ pstart);
+}
+
static const struct address_space_operations erofs_fscache_blob_aops = {
};

--
2.27.0