powerpc/fadump: Reorganize /sys/kernel/fadump_* sysfs files

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 backward compatibility a
symlink has been added for every sysfs that has moved to new location.

As the FADump sysfs files are now part of a 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>
Tested-by: Michal Suchanek <msuchanek@suse.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20191211160910.21656-4-sourabhjain@linux.ibm.com

Documentation/ABI/testing/sysfs-kernel-fadump

+What:		/sys/kernel/fadump/*
+Date:		Dec 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:		Dec 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:		Dec 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:		Dec 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.

arch/powerpc/kernel/fadump.c

@@ -36,6 +36,8 @@ static struct fw_dump fw_dump;
 
 static void __init fadump_reserve_crash_area(u64 base);
 
+struct kobject *fadump_kobj;
+
 #ifndef CONFIG_PRESERVE_FA_DUMP
 static DEFINE_MUTEX(fadump_mutex);
 struct fadump_mrange_info crash_mrange_info = { "crash", NULL, 0, 0, 0 };
@@ -1323,9 +1325,9 @@ static void fadump_invalidate_release_mem(void)
 	fw_dump.ops->fadump_init_mem_struct(&fw_dump);
 }
 
-static ssize_t fadump_release_memory_store(struct kobject *kobj,
-					struct kobj_attribute *attr,
-					const char *buf, size_t count)
+static ssize_t release_mem_store(struct kobject *kobj,
+				 struct kobj_attribute *attr,
+				 const char *buf, size_t count)
 {
 	int input = -1;
 
@@ -1350,23 +1352,33 @@ static ssize_t fadump_release_memory_store(struct kobject *kobj,
 	return count;
 }
 
-static ssize_t fadump_enabled_show(struct kobject *kobj,
-					struct kobj_attribute *attr,
-					char *buf)
+/* Release the reserved memory and disable the FADump */
+static void unregister_fadump(void)
+{
+	fadump_cleanup();
+	fadump_release_memory(fw_dump.reserve_dump_area_start,
+			      fw_dump.reserve_dump_area_size);
+	fw_dump.fadump_enabled = 0;
+	kobject_put(fadump_kobj);
+}
+
+static ssize_t enabled_show(struct kobject *kobj,
+			    struct kobj_attribute *attr,
+			    char *buf)
 {
 	return sprintf(buf, "%d\n", fw_dump.fadump_enabled);
 }
 
-static ssize_t fadump_register_show(struct kobject *kobj,
-					struct kobj_attribute *attr,
-					char *buf)
+static ssize_t registered_show(struct kobject *kobj,
+			       struct kobj_attribute *attr,
+			       char *buf)
 {
 	return sprintf(buf, "%d\n", fw_dump.dump_registered);
 }
 
-static ssize_t fadump_register_store(struct kobject *kobj,
-					struct kobj_attribute *attr,
-					const char *buf, size_t count)
+static ssize_t registered_store(struct kobject *kobj,
+				struct kobj_attribute *attr,
+				const char *buf, size_t count)
 {
 	int ret = 0;
 	int input = -1;
@@ -1418,15 +1430,17 @@ static int fadump_region_show(struct seq_file *m, void *private)
 	return 0;
 }
 
-static struct kobj_attribute fadump_release_attr = __ATTR(fadump_release_mem,
-						0200, NULL,
-						fadump_release_memory_store);
-static struct kobj_attribute fadump_attr = __ATTR(fadump_enabled,
-						0444, fadump_enabled_show,
-						NULL);
-static struct kobj_attribute fadump_register_attr = __ATTR(fadump_registered,
-						0644, fadump_register_show,
-						fadump_register_store);
+static struct kobj_attribute release_attr = __ATTR_WO(release_mem);
+static struct kobj_attribute enable_attr = __ATTR_RO(enabled);
+static struct kobj_attribute register_attr = __ATTR_RW(registered);
+
+static struct attribute *fadump_attrs[] = {
+	&enable_attr.attr,
+	&register_attr.attr,
+	NULL,
+};
+
+ATTRIBUTE_GROUPS(fadump);
 
 DEFINE_SHOW_ATTRIBUTE(fadump_region);
 
@@ -1435,16 +1449,11 @@ static void fadump_init_files(void)
 	struct dentry *debugfs_file;
 	int rc = 0;
 
-	rc = sysfs_create_file(kernel_kobj, &fadump_attr.attr);
-	if (rc)
-		printk(KERN_ERR "fadump: unable to create sysfs file"
-			" fadump_enabled (%d)\n", rc);
-
-	rc = sysfs_create_file(kernel_kobj, &fadump_register_attr.attr);
-	if (rc)
-		printk(KERN_ERR "fadump: unable to create sysfs file"
-			" fadump_registered (%d)\n", rc);
-
+	fadump_kobj = kobject_create_and_add("fadump", kernel_kobj);
+	if (!fadump_kobj) {
+		pr_err("failed to create fadump kobject\n");
+		return;
+	}
 	debugfs_file = debugfs_create_file("fadump_region", 0444,
 					powerpc_debugfs_root, NULL,
 					&fadump_region_fops);
@@ -1453,10 +1462,52 @@ static void fadump_init_files(void)
 				" fadump_region\n");
 
 	if (fw_dump.dump_active) {
-		rc = sysfs_create_file(kernel_kobj, &fadump_release_attr.attr);
+		rc = sysfs_create_file(fadump_kobj, &release_attr.attr);
+		if (rc)
+			pr_err("unable to create release_mem sysfs file (%d)\n",
+			       rc);
+	}
+
+	rc = sysfs_create_groups(fadump_kobj, fadump_groups);
+	if (rc) {
+		pr_err("sysfs group creation failed (%d), unregistering FADump",
+		       rc);
+		unregister_fadump();
+		return;
+	}
+
+	/*
+	 * The FADump sysfs are moved from kernel_kobj to fadump_kobj need to
+	 * create symlink at old location to maintain backward compatibility.
+	 *
+	 *      - fadump_enabled -> fadump/enabled
+	 *      - fadump_registered -> fadump/registered
+	 *      - fadump_release_mem -> fadump/release_mem
+	 */
+	rc = compat_only_sysfs_link_entry_to_kobj(kernel_kobj, fadump_kobj,
+						  "enabled", "fadump_enabled");
+	if (rc) {
+		pr_err("unable to create fadump_enabled symlink (%d)", rc);
+		return;
+	}
+
+	rc = compat_only_sysfs_link_entry_to_kobj(kernel_kobj, fadump_kobj,
+						  "registered",
+						  "fadump_registered");
+	if (rc) {
+		pr_err("unable to create fadump_registered symlink (%d)", rc);
+		sysfs_remove_link(kernel_kobj, "fadump_enabled");
+		return;
+	}
+
+	if (fw_dump.dump_active) {
+		rc = compat_only_sysfs_link_entry_to_kobj(kernel_kobj,
+							  fadump_kobj,
+							  "release_mem",
+							  "fadump_release_mem");
 		if (rc)
-			printk(KERN_ERR "fadump: unable to create sysfs file"
-				" fadump_release_mem (%d)\n", rc);
+			pr_err("unable to create fadump_release_mem symlink (%d)",
+			       rc);
 	}
 	return;
 }