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SubjectRe: [PATCH v3 2/4] powerpc/fadump: reorganize /sys/kernel/fadump_* sysfs files
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

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