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, 54 insertions, 0 deletions

diff --git a/drivers/char/tpm/tpmrm-dev.c b/drivers/char/tpm/tpmrm-dev.c
new file mode 100644
index 000000000..19e8f2779
--- /dev/null
+++ b/drivers/char/tpm/tpmrm-dev.c
@@ -0,0 +1,54 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2017 James.Bottomley@HansenPartnership.com
+ */
+#include <linux/slab.h>
+#include "tpm-dev.h"
+
+struct tpmrm_priv {
+	struct file_priv priv;
+	struct tpm_space space;
+};
+
+static int tpmrm_open(struct inode *inode, struct file *file)
+{
+	struct tpm_chip *chip;
+	struct tpmrm_priv *priv;
+	int rc;
+
+	chip = container_of(inode->i_cdev, struct tpm_chip, cdevs);
+	priv = kzalloc_obj(*priv);
+	if (priv == NULL)
+		return -ENOMEM;
+
+	rc = tpm2_init_space(&priv->space, TPM2_SPACE_BUFFER_SIZE);
+	if (rc) {
+		kfree(priv);
+		return -ENOMEM;
+	}
+
+	tpm_common_open(file, chip, &priv->priv, &priv->space);
+
+	return nonseekable_open(inode, file);
+}
+
+static int tpmrm_release(struct inode *inode, struct file *file)
+{
+	struct file_priv *fpriv = file->private_data;
+	struct tpmrm_priv *priv = container_of(fpriv, struct tpmrm_priv, priv);
+
+	tpm_common_release(file, fpriv);
+	tpm2_del_space(fpriv->chip, &priv->space);
+	kfree(priv);
+
+	return 0;
+}
+
+const struct file_operations tpmrm_fops = {
+	.owner = THIS_MODULE,
+	.open = tpmrm_open,
+	.read = tpm_common_read,
+	.write = tpm_common_write,
+	.poll = tpm_common_poll,
+	.release = tpmrm_release,
+};