[RFC PATCH 34/53] netfs: Make netfs_skip_folio_read() take account of blocksize

[David Howells <dhowells@xxxxxxxxxx>]

Make netfs_skip_folio_read() take account of blocksize such as crypto
blocksize.

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Jeff Layton <jlayton@xxxxxxxxxx>
cc: linux-cachefs@xxxxxxxxxx
cc: linux-fsdevel@xxxxxxxxxxxxxxx
cc: linux-mm@xxxxxxxxx
---
 fs/netfs/buffered_read.c | 32 +++++++++++++++++++++-----------
 1 file changed, 21 insertions(+), 11 deletions(-)

diff --git a/fs/netfs/buffered_read.c b/fs/netfs/buffered_read.c
index e06461ef0bfa..de696aaaefbd 100644
--- a/fs/netfs/buffered_read.c
+++ b/fs/netfs/buffered_read.c
@@ -337,6 +337,7 @@ EXPORT_SYMBOL(netfs_read_folio);
 
 /*
  * Prepare a folio for writing without reading first
+ * @ctx: File context
  * @folio: The folio being prepared
  * @pos: starting position for the write
  * @len: length of write
@@ -350,32 +351,41 @@ EXPORT_SYMBOL(netfs_read_folio);
  * If any of these criteria are met, then zero out the unwritten parts
  * of the folio and return true. Otherwise, return false.
  */
-static bool netfs_skip_folio_read(struct folio *folio, loff_t pos, size_t len,
-				 bool always_fill)
+static bool netfs_skip_folio_read(struct netfs_inode *ctx, struct folio *folio,
+				  loff_t pos, size_t len, bool always_fill)
 {
 	struct inode *inode = folio_inode(folio);
-	loff_t i_size = i_size_read(inode);
+	loff_t i_size = i_size_read(inode), low, high;
 	size_t offset = offset_in_folio(folio, pos);
 	size_t plen = folio_size(folio);
+	size_t min_bsize = 1UL << ctx->min_bshift;
+
+	if (likely(min_bsize == 1)) {
+		low = folio_file_pos(folio);
+		high = low + plen;
+	} else {
+		low = round_down(pos, min_bsize);
+		high = round_up(pos + len, min_bsize);
+	}
 
 	if (unlikely(always_fill)) {
-		if (pos - offset + len <= i_size)
-			return false; /* Page entirely before EOF */
+		if (low < i_size)
+			return false; /* Some part of the block before EOF */
 		zero_user_segment(&folio->page, 0, plen);
 		folio_mark_uptodate(folio);
 		return true;
 	}
 
-	/* Full folio write */
-	if (offset == 0 && len >= plen)
+	/* Full page write */
+	if (pos == low && high == pos + len)
 		return true;
 
-	/* Page entirely beyond the end of the file */
-	if (pos - offset >= i_size)
+	/* pos beyond last page in the file */
+	if (low >= i_size)
 		goto zero_out;
 
 	/* Write that covers from the start of the folio to EOF or beyond */
-	if (offset == 0 && (pos + len) >= i_size)
+	if (pos == low && (pos + len) >= i_size)
 		goto zero_out;
 
 	return false;
@@ -454,7 +464,7 @@ int netfs_write_begin(struct netfs_inode *ctx,
 	 * to preload the granule.
 	 */
 	if (!netfs_is_cache_enabled(ctx) &&
-	    netfs_skip_folio_read(folio, pos, len, false)) {
+	    netfs_skip_folio_read(ctx, folio, pos, len, false)) {
 		netfs_stat(&netfs_n_rh_write_zskip);
 		goto have_folio_no_wait;
 	}