linux-kernel - [PATCH v4 1/3] configfs: Restore the kernel v5.13 text attribute write behavior

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Message-Id: <20210805043503.20252-2-bvanassche@acm.org>
Date:   Wed,  4 Aug 2021 21:35:01 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Christoph Hellwig <hch@....de>
Cc:     Joel Becker <jlbec@...lplan.org>, linux-kernel@...r.kernel.org,
        Bodo Stroesser <bostroesser@...il.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        Bart Van Assche <bvanassche@....org>,
        Yanko Kaneti <yaneti@...lera.com>
Subject: [PATCH v4 1/3] configfs: Restore the kernel v5.13 text attribute write behavior

Instead of appending new text attribute data at the offset specified by the
write() system call, only pass the newly written data to the .store()
callback.

Cc: Bodo Stroesser <bostroesser@...il.com>
Cc: Martin K. Petersen <martin.petersen@...cle.com>
Cc: Yanko Kaneti <yaneti@...lera.com>
Cc: Brendan Higgins <brendanhiggins@...gle.com>
Reported-by: Bodo Stroesser <bostroesser@...il.com>
Tested-by: Bodo Stroesser <bostroesser@...il.com>
Signed-off-by: Bart Van Assche <bvanassche@....org>
---
 fs/configfs/file.c | 18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

diff --git a/fs/configfs/file.c b/fs/configfs/file.c
index 5a0be9985bae..0ad32150611e 100644
--- a/fs/configfs/file.c
+++ b/fs/configfs/file.c
@@ -177,28 +177,22 @@ static ssize_t configfs_bin_read_iter(struct kiocb *iocb, struct iov_iter *to)
 	return retval;
 }
 
-/* Fill [buffer, buffer + pos) with data coming from @from. */
-static int fill_write_buffer(struct configfs_buffer *buffer, loff_t pos,
+/* Fill @buffer with data coming from @from. */
+static int fill_write_buffer(struct configfs_buffer *buffer,
 			     struct iov_iter *from)
 {
-	loff_t to_copy;
 	int copied;
-	u8 *to;
 
 	if (!buffer->page)
 		buffer->page = (char *)__get_free_pages(GFP_KERNEL, 0);
 	if (!buffer->page)
 		return -ENOMEM;
 
-	to_copy = SIMPLE_ATTR_SIZE - 1 - pos;
-	if (to_copy <= 0)
-		return 0;
-	to = buffer->page + pos;
-	copied = copy_from_iter(to, to_copy, from);
+	copied = copy_from_iter(buffer->page, SIMPLE_ATTR_SIZE - 1, from);
 	buffer->needs_read_fill = 1;
 	/* if buf is assumed to contain a string, terminate it by \0,
 	 * so e.g. sscanf() can scan the string easily */
-	to[copied] = 0;
+	buffer->page[copied] = 0;
 	return copied ? : -EFAULT;
 }
 
@@ -227,10 +221,10 @@ static ssize_t configfs_write_iter(struct kiocb *iocb, struct iov_iter *from)
 {
 	struct file *file = iocb->ki_filp;
 	struct configfs_buffer *buffer = file->private_data;
-	ssize_t len;
+	int len;
 
 	mutex_lock(&buffer->mutex);
-	len = fill_write_buffer(buffer, iocb->ki_pos, from);
+	len = fill_write_buffer(buffer, from);
 	if (len > 0)
 		len = flush_write_buffer(file, buffer, len);
 	if (len > 0)