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Message-Id: <20241103-sysfs-const-bin_attr-v2-2-71110628844c@weissschuh.net>
Date: Sun, 03 Nov 2024 17:03:31 +0000
From: Thomas Weißschuh <linux@...ssschuh.net>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
 "Rafael J. Wysocki" <rafael@...nel.org>, 
 Bjorn Helgaas <bhelgaas@...gle.com>, 
 Srinivas Kandagatla <srinivas.kandagatla@...aro.org>, 
 Davidlohr Bueso <dave@...olabs.net>, 
 Jonathan Cameron <jonathan.cameron@...wei.com>, 
 Dave Jiang <dave.jiang@...el.com>, 
 Alison Schofield <alison.schofield@...el.com>, 
 Vishal Verma <vishal.l.verma@...el.com>, Ira Weiny <ira.weiny@...el.com>, 
 Alex Deucher <alexander.deucher@....com>, 
 Christian König <christian.koenig@....com>, 
 Xinhui Pan <Xinhui.Pan@....com>, David Airlie <airlied@...il.com>, 
 Simona Vetter <simona@...ll.ch>, 
 Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>, 
 Jason Gunthorpe <jgg@...pe.ca>, Leon Romanovsky <leon@...nel.org>, 
 Tudor Ambarus <tudor.ambarus@...aro.org>, 
 Pratyush Yadav <pratyush@...nel.org>, Michael Walle <mwalle@...nel.org>, 
 Miquel Raynal <miquel.raynal@...tlin.com>, 
 Richard Weinberger <richard@....at>, Vignesh Raghavendra <vigneshr@...com>, 
 Naveen Krishna Chatradhi <naveenkrishna.chatradhi@....com>, 
 Carlos Bilbao <carlos.bilbao.osdev@...il.com>, 
 Hans de Goede <hdegoede@...hat.com>, 
 Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>, 
 "David E. Box" <david.e.box@...ux.intel.com>, 
 "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>, 
 "Martin K. Petersen" <martin.petersen@...cle.com>, 
 Richard Henderson <richard.henderson@...aro.org>, 
 Matt Turner <mattst88@...il.com>, Frederic Barrat <fbarrat@...ux.ibm.com>, 
 Andrew Donnellan <ajd@...ux.ibm.com>, Arnd Bergmann <arnd@...db.de>, 
 Logan Gunthorpe <logang@...tatee.com>, 
 "K. Y. Srinivasan" <kys@...rosoft.com>, 
 Haiyang Zhang <haiyangz@...rosoft.com>, Wei Liu <wei.liu@...nel.org>, 
 Dexuan Cui <decui@...rosoft.com>
Cc: Dan Williams <dan.j.williams@...el.com>, linux-kernel@...r.kernel.org, 
 linux-pci@...r.kernel.org, linux-cxl@...r.kernel.org, 
 amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org, 
 linux-rdma@...r.kernel.org, linux-mtd@...ts.infradead.org, 
 platform-driver-x86@...r.kernel.org, linux-scsi@...r.kernel.org, 
 linux-usb@...r.kernel.org, linux-alpha@...r.kernel.org, 
 linuxppc-dev@...ts.ozlabs.org, linux-hyperv@...r.kernel.org, 
 Thomas Weißschuh <linux@...ssschuh.net>
Subject: [PATCH v2 02/10] sysfs: introduce callback
 attribute_group::bin_size

Several drivers need to dynamically calculate the size of an binary
attribute. Currently this is done by assigning attr->size from the
is_bin_visible() callback.

This has drawbacks:
* It is not documented.
* A single attribute can be instantiated multiple times, overwriting the
  shared size field.
* It prevents the structure to be moved to read-only memory.

Introduce a new dedicated callback to calculate the size of the
attribute.

Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
---
 fs/sysfs/group.c      | 2 ++
 include/linux/sysfs.h | 8 ++++++++
 2 files changed, 10 insertions(+)

diff --git a/fs/sysfs/group.c b/fs/sysfs/group.c
index 45b2e92941da1f49dcc71af3781317c61480c956..8b01a7eda5fb3239e138372417d01967c7a3f122 100644
--- a/fs/sysfs/group.c
+++ b/fs/sysfs/group.c
@@ -98,6 +98,8 @@ static int create_files(struct kernfs_node *parent, struct kobject *kobj,
 				if (!mode)
 					continue;
 			}
+			if (grp->bin_size)
+				size = grp->bin_size(kobj, *bin_attr, i);
 
 			WARN(mode & ~(SYSFS_PREALLOC | 0664),
 			     "Attribute %s: Invalid permissions 0%o\n",
diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index c4e64dc112063f7cb89bf66059d0338716089e87..4746cccb95898b24df6f53de9421ea7649b5568f 100644
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -87,6 +87,11 @@ do {							\
  *		SYSFS_GROUP_VISIBLE() when assigning this callback to
  *		specify separate _group_visible() and _attr_visible()
  *		handlers.
+ * @bin_size:
+ *		Optional: Function to return the size of a binary attribute
+ *		of the group. Will be called repeatedly for each binary
+ *		attribute in the group. Overwrites the size field embedded
+ *		inside the attribute itself.
  * @attrs:	Pointer to NULL terminated list of attributes.
  * @bin_attrs:	Pointer to NULL terminated list of binary attributes.
  *		Either attrs or bin_attrs or both must be provided.
@@ -97,6 +102,9 @@ struct attribute_group {
 					      struct attribute *, int);
 	umode_t			(*is_bin_visible)(struct kobject *,
 						  struct bin_attribute *, int);
+	size_t			(*bin_size)(struct kobject *,
+					    const struct bin_attribute *,
+					    int);
 	struct attribute	**attrs;
 	struct bin_attribute	**bin_attrs;
 };

-- 
2.47.0


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