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Date:   Sun, 24 Nov 2019 19:40:59 +0100
From:   Michal =?iso-8859-1?Q?Such=E1nek?= <msuchanek@suse.de>
To:     Sourabh Jain <sourabhjain@linux.ibm.com>
Cc:     linux-doc@vger.kernel.org, mahesh@linux.vnet.ibm.com,
        corbet@lwn.net, linux-kernel@vger.kernel.org,
        linuxppc-dev@ozlabs.org, hbathini@linux.ibm.com
Subject: Re: [PATCH v3 2/4] powerpc/fadump: reorganize /sys/kernel/fadump_*
 sysfs files
Message-ID: <20191124184059.GP11661@kitsune.suse.cz>
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 <20191109125933.GF1384@kitsune.suse.cz>
 <8c1ec297-0c34-12de-2528-be436697215a@linux.ibm.com>
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On Sat, Nov 16, 2019 at 08:07:29PM +0530, Sourabh Jain wrote:
> 
> 
> On 11/9/19 6:29 PM, Michal Suchánek wrote:
> > On Sat, Nov 09, 2019 at 05:53:37PM +0530, Sourabh Jain wrote:
> >> As the number of FADump sysfs files increases it is hard to manage all of
> >> them inside /sys/kernel directory. It's better to have all the FADump
> >> related sysfs files in a dedicated directory /sys/kernel/fadump. But in
> >> order to maintain the backward compatibility the /sys/kernel/fadump_*
> >> sysfs files are replicated inside /sys/kernel/fadump/ and eventually get
> >> removed in future.
> >>
> >> As the FADump sysfs files are now part of dedicated directory there is no
> >> need to prefix their name with fadump_, hence sysfs file names are also
> >> updated. For example fadump_enabled sysfs file is now referred as enabled.
> >>
> >> Also consolidate ABI documentation for all the FADump sysfs files in a
> >> single file Documentation/ABI/testing/sysfs-kernel-fadump.
> >>
> >> Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>
> >> ---
> >>  Documentation/ABI/testing/sysfs-kernel-fadump | 41 +++++++++++++++++++
> >>  arch/powerpc/kernel/fadump.c                  | 38 +++++++++++++++++
> >>  arch/powerpc/platforms/powernv/opal-core.c    | 10 +++--
> >>  3 files changed, 86 insertions(+), 3 deletions(-)
> >>  create mode 100644 Documentation/ABI/testing/sysfs-kernel-fadump
> >>
> >> diff --git a/Documentation/ABI/testing/sysfs-kernel-fadump b/Documentation/ABI/testing/sysfs-kernel-fadump
> >> new file mode 100644
> >> index 000000000000..a77f1a5ba389
> >> --- /dev/null
> >> +++ b/Documentation/ABI/testing/sysfs-kernel-fadump
> >> @@ -0,0 +1,41 @@
> >> +What:		/sys/kernel/fadump/*
> >> +Date:		Nov 2019
> >> +Contact:	linuxppc-dev@lists.ozlabs.org
> >> +Description:
> >> +		The /sys/kernel/fadump/* is a collection of FADump sysfs
> >> +		file provide information about the configuration status
> >> +		of Firmware Assisted Dump (FADump).
> >> +
> >> +What:		/sys/kernel/fadump/enabled
> >> +Date:		Nov 2019
> >> +Contact:	linuxppc-dev@lists.ozlabs.org
> >> +Description:	read only
> >> +		Primarily used to identify whether the FADump is enabled in
> >> +		the kernel or not.
> >> +User:		Kdump service
> >> +
> >> +What:		/sys/kernel/fadump/registered
> >> +Date:		Nov 2019
> >> +Contact:	linuxppc-dev@lists.ozlabs.org
> >> +Description:	read/write
> >> +		Helps to control the dump collect feature from userspace.
> >> +		Setting 1 to this file enables the system to collect the
> >> +		dump and 0 to disable it.
> >> +User:		Kdump service
> >> +
> >> +What:		/sys/kernel/fadump/release_mem
> >> +Date:		Nov 2019
> >> +Contact:	linuxppc-dev@lists.ozlabs.org
> >> +Description:	write only
> >> +		This is a special sysfs file and only available when
> >> +		the system is booted to capture the vmcore using FADump.
> >> +		It is used to release the memory reserved by FADump to
> >> +		save the crash dump.
> >> +
> >> +What:		/sys/kernel/fadump/release_opalcore
> >> +Date:		Nov 2019
> >> +Contact:	linuxppc-dev@lists.ozlabs.org
> >> +Description:	write only
> >> +		The sysfs file is available when the system is booted to
> >> +		collect the dump on OPAL based machine. It used to release
> >> +		the memory used to collect the opalcore.
> >> diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c
> >> index ed59855430b9..a9591def0c84 100644
> >> --- a/arch/powerpc/kernel/fadump.c
> >> +++ b/arch/powerpc/kernel/fadump.c
> >> @@ -1418,6 +1418,9 @@ static int fadump_region_show(struct seq_file *m, void *private)
> >>  	return 0;
> >>  }
> >>  
> >> +struct kobject *fadump_kobj;
> >> +EXPORT_SYMBOL_GPL(fadump_kobj);
> >> +
> >>  static struct kobj_attribute fadump_release_attr = __ATTR(fadump_release_mem,
> >>  						0200, NULL,
> >>  						fadump_release_memory_store);
> >> @@ -1428,6 +1431,16 @@ static struct kobj_attribute fadump_register_attr = __ATTR(fadump_registered,
> >>  						0644, fadump_register_show,
> >>  						fadump_register_store);
> >>  
> >> +static struct kobj_attribute release_attr = __ATTR(release_mem,
> >> +						0200, NULL,
> >> +						fadump_release_memory_store);
> >> +static struct kobj_attribute enable_attr = __ATTR(enabled,
> >> +						0444, fadump_enabled_show,
> >> +						NULL);
> >> +static struct kobj_attribute register_attr = __ATTR(registered,
> >> +						0644, fadump_register_show,
> >> +						fadump_register_store);
> >> +
> >>  DEFINE_SHOW_ATTRIBUTE(fadump_region);
> >>  
> >>  static void fadump_init_files(void)
> >> @@ -1435,6 +1448,11 @@ static void fadump_init_files(void)
> >>  	struct dentry *debugfs_file;
> >>  	int rc = 0;
> >>  
> >> +	fadump_kobj = kobject_create_and_add("fadump", kernel_kobj);
> >> +	if (!fadump_kobj) {
> >> +		pr_err("failed to create fadump kobject\n");
> >> +		return;
> >> +	}
> >>  	rc = sysfs_create_file(kernel_kobj, &fadump_attr.attr);
> >>  	if (rc)
> >>  		printk(KERN_ERR "fadump: unable to create sysfs file"
> >> @@ -1458,6 +1476,26 @@ static void fadump_init_files(void)
> >>  			printk(KERN_ERR "fadump: unable to create sysfs file"
> >>  				" fadump_release_mem (%d)\n", rc);
> >>  	}
> >> +	/* Replicating the following sysfs attributes under FADump kobject.
> >> +	 *
> >> +	 *	- fadump_enabled -> enabled
> >> +	 *	- fadump_registered -> registered
> >> +	 *	- fadump_release_mem -> release_mem
> >> +	 */
> >> +	rc = sysfs_create_file(fadump_kobj, &enable_attr.attr);
> >> +	if (rc)
> >> +		pr_err("unable to create enabled sysfs file (%d)\n",
> >> +		       rc);
> >> +	rc = sysfs_create_file(fadump_kobj, &register_attr.attr);
> >> +	if (rc)
> >> +		pr_err("unable to create registered sysfs file (%d)\n",
> >> +		       rc);
> >> +	if (fw_dump.dump_active) {
> >> +		rc = sysfs_create_file(fadump_kobj, &release_attr.attr);
> >> +		if (rc)
> >> +			pr_err("unable to create release_mem sysfs file (%d)\n",
> >> +			       rc);
> >> +	}
> >>  	return;
> >>  }
> > Hello,
> > 
> 
> I’m so sorry for taking this long to write you back. 
> 
> > wouldn't it make more sense to create the files in the new location and
> > add a symlink at the old location?
> 
> There are APIs which allow to create a symlink for an entire kobject but
> I did not find a way to create symlink of an individual sysfs file.
> 
> Do you have any approach in mind to achieve the same?

There is at least one example of plain symlink:

find /sys -type l -xtype f
/sys/kernel/security/evm

If there is no interface to do one sanely duplicationg the files is
better than nothing.

Thanks

Michal