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, 53 insertions, 0 deletions

diff --git a/scripts/include/xalloc.h b/scripts/include/xalloc.h
new file mode 100644
index 000000000..cdadb07d0
--- /dev/null
+++ b/scripts/include/xalloc.h
@@ -0,0 +1,53 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef XALLOC_H
+#define XALLOC_H
+
+#include <stdlib.h>
+#include <string.h>
+
+static inline void *xmalloc(size_t size)
+{
+	void *p = malloc(size);
+
+	if (!p)
+		exit(1);
+	return p;
+}
+
+static inline void *xcalloc(size_t nmemb, size_t size)
+{
+	void *p = calloc(nmemb, size);
+
+	if (!p)
+		exit(1);
+	return p;
+}
+
+static inline void *xrealloc(void *p, size_t size)
+{
+	p = realloc(p, size);
+	if (!p)
+		exit(1);
+	return p;
+}
+
+static inline char *xstrdup(const char *s)
+{
+	char *p = strdup(s);
+
+	if (!p)
+		exit(1);
+	return p;
+}
+
+static inline char *xstrndup(const char *s, size_t n)
+{
+	char *p = strndup(s, n);
+
+	if (!p)
+		exit(1);
+	return p;
+}
+
+#endif /* XALLOC_H */