linux-kernel - [PATCH 2/9] sysfs: add growable flag to struct bin

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Message-Id: <20211007000954.30621-3-zev@bewilderbeest.net>
Date:   Wed,  6 Oct 2021 17:09:47 -0700
From:   Zev Weiss <zev@...ilderbeest.net>
To:     openbmc@...ts.ozlabs.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jeremy Kerr <jk@...econstruct.com.au>,
        Joel Stanley <joel@....id.au>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        Zev Weiss <zev@...ilderbeest.net>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/9] sysfs: add growable flag to struct bin_attribute

Previously, sysfs_kf_bin_write() unconditionally disallowed writing
past the existing size of the file.  In order to support mutable
device-tree status properties (which are bin_attributes), we need to
be able to write a longer value over a shorter existing one
(e.g. writing "reserved\n" over "okay\0").  bin_attributes that
require this can now set the growable flag to disable that checking
and allow arbitrary amounts of data to be written at arbitrary
offsets.

Signed-off-by: Zev Weiss <zev@...ilderbeest.net>
---
 fs/sysfs/file.c       | 2 +-
 include/linux/sysfs.h | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index b2b85be95adf..156df003ea8f 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -147,7 +147,7 @@ static ssize_t sysfs_kf_bin_write(struct kernfs_open_file *of, char *buf,
 	struct kobject *kobj = of->kn->parent->priv;
 	loff_t size = file_inode(of->file)->i_size;
 
-	if (size) {
+	if (!battr->growable && size) {
 		if (size <= pos)
 			return -EFBIG;
 		count = min_t(ssize_t, count, size - pos);
diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index 49de5189cf88..f8a56094c6c9 100644
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -175,6 +175,7 @@ struct address_space;
 struct bin_attribute {
 	struct attribute	attr;
 	size_t			size;
+	bool			growable:1;
 	void			*private;
 	struct address_space *(*f_mapping)(void);
 	ssize_t (*read)(struct file *, struct kobject *, struct bin_attribute *,
-- 
2.33.0