netfs: zero the tail of a short DIO/unbuffered readgrafted

The buffered read collector zero-fills the tail of a short read that
stops below the inode's i_size (netfs_clear_unread()), so a read that
races an extending write still returns the expected number of bytes.
The non-buffered collector path does no such thing: it just records
how much was transferred.

Add the same zero-fill for the non-buffered case, gated on
NETFS_SREQ_CLEAR_TAIL: a subreq's source sets that flag when a short
result from it is known to be safe to treat as a hole, as opposed to
NETFS_SREQ_HIT_EOF, which means the read genuinely ran off the end of
the file and should be reported short as-is. Only CLEAR_TAIL should
zero-fill here; a real EOF must stay a real short read.

No source currently sets CLEAR_TAIL on an unbuffered/DIO subrequest,
so this is inert on its own -- a following change teaches cifs to set
it in the one case that needs it.

Fixes: e2d46f2ec332 ("netfs: Change the read result collector to only use one work item")
Reviewed-by: David Howells <dhowells@redhat.com>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Bharath SM <bharathsm@microsoft.com>
Cc: stable@vger.kernel.org

1 files changed, 75 insertions, 0 deletions

diff --git a/drivers/md/bcache/features.c b/drivers/md/bcache/features.c
new file mode 100644
index 000000000..634922c56
--- /dev/null
+++ b/drivers/md/bcache/features.c
@@ -0,0 +1,75 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Feature set bits and string conversion.
+ * Inspired by ext4's features compat/incompat/ro_compat related code.
+ *
+ * Copyright 2020 Coly Li <colyli@suse.de>
+ *
+ */
+#include "bcache_ondisk.h"
+#include "bcache.h"
+#include "features.h"
+
+struct feature {
+	int		compat;
+	unsigned int	mask;
+	const char	*string;
+};
+
+static struct feature feature_list[] = {
+	{BCH_FEATURE_INCOMPAT, BCH_FEATURE_INCOMPAT_LOG_LARGE_BUCKET_SIZE,
+		"large_bucket"},
+	{0, 0, NULL },
+};
+
+#define compose_feature_string(type)				\
+({									\
+	struct feature *f;						\
+	bool first = true;						\
+									\
+	for (f = &feature_list[0]; f->compat != 0; f++) {		\
+		if (f->compat != BCH_FEATURE_ ## type)			\
+			continue;					\
+		if (BCH_HAS_ ## type ## _FEATURE(&c->cache->sb, f->mask)) {	\
+			if (first) {					\
+				out += snprintf(out, buf + size - out,	\
+						"[");	\
+			} else {					\
+				out += snprintf(out, buf + size - out,	\
+						" [");			\
+			}						\
+		} else if (!first) {					\
+			out += snprintf(out, buf + size - out, " ");	\
+		}							\
+									\
+		out += snprintf(out, buf + size - out, "%s", f->string);\
+									\
+		if (BCH_HAS_ ## type ## _FEATURE(&c->cache->sb, f->mask))	\
+			out += snprintf(out, buf + size - out, "]");	\
+									\
+		first = false;						\
+	}								\
+	if (!first)							\
+		out += snprintf(out, buf + size - out, "\n");		\
+})
+
+int bch_print_cache_set_feature_compat(struct cache_set *c, char *buf, int size)
+{
+	char *out = buf;
+	compose_feature_string(COMPAT);
+	return out - buf;
+}
+
+int bch_print_cache_set_feature_ro_compat(struct cache_set *c, char *buf, int size)
+{
+	char *out = buf;
+	compose_feature_string(RO_COMPAT);
+	return out - buf;
+}
+
+int bch_print_cache_set_feature_incompat(struct cache_set *c, char *buf, int size)
+{
+	char *out = buf;
+	compose_feature_string(INCOMPAT);
+	return out - buf;
+}