pstore: new filesystem interface to platform persistent storage

Some platforms have a small amount of non-volatile storage that
can be used to store information useful to diagnose the cause of
a system crash.  This is the generic part of a file system interface
that presents information from the crash as a series of files in
/dev/pstore.  Once the information has been seen, the underlying
storage is freed by deleting the files.

Signed-off-by: Tony Luck <[email protected]>

Documentation/ABI/testing/pstore

@@ -0,0 +1,35 @@
+Where:		/dev/pstore/...
+Date:		January 2011
+Kernel Version: 2.6.38
+Contact:	[email protected]
+Description:	Generic interface to platform dependent persistent storage.
+
+		Platforms that provide a mechanism to preserve some data
+		across system reboots can register with this driver to
+		provide a generic interface to show records captured in
+		the dying moments.  In the case of a panic the last part
+		of the console log is captured, but other interesting
+		data can also be saved.
+
+		# mount -t pstore - /dev/pstore
+
+		$ ls -l /dev/pstore
+		total 0
+		-r--r--r-- 1 root root 7896 Nov 30 15:38 dmesg-erst-1
+
+		Different users of this interface will result in different
+		filename prefixes.  Currently two are defined:
+
+		"dmesg"	- saved console log
+		"mce"	- architecture dependent data from fatal h/w error
+
+		Once the information in a file has been read, removing
+		the file will signal to the underlying persistent storage
+		device that it can reclaim the space for later re-use.
+
+		$ rm /dev/pstore/dmesg-erst-1
+
+		The expectation is that all files in /dev/pstore
+		will be saved elsewhere and erased from persistent store
+		soon after boot to free up space ready for the next
+		catastrophe.

Documentation/ABI/testing/sysfs-fs-pstore

@@ -0,0 +1,7 @@
+What:		/sys/fs/pstore/kmsg_bytes
+Date:		January 2011
+Kernel Version: 2.6.38
+Contact:	"Tony Luck" <[email protected]>
+Description:
+		Controls amount of console log that will be saved
+		to persistent store on oops/panic.

fs/Kconfig

@@ -188,6 +188,7 @@ source "fs/omfs/Kconfig"
 source "fs/hpfs/Kconfig"
 source "fs/qnx4/Kconfig"
 source "fs/romfs/Kconfig"
+source "fs/pstore/Kconfig"
 source "fs/sysv/Kconfig"
 source "fs/ufs/Kconfig"
 source "fs/exofs/Kconfig"

fs/Makefile

@@ -121,3 +121,4 @@ obj-$(CONFIG_BTRFS_FS)		+= btrfs/
 obj-$(CONFIG_GFS2_FS)           += gfs2/
 obj-$(CONFIG_EXOFS_FS)          += exofs/
 obj-$(CONFIG_CEPH_FS)		+= ceph/
+obj-$(CONFIG_PSTORE)		+= pstore/

fs/pstore/Kconfig

@@ -0,0 +1,13 @@
+config PSTORE
+	bool "Persistant store support"
+	default n
+	help
+	   This option enables generic access to platform level
+	   persistent storage via "pstore" filesystem that can
+	   be mounted as /dev/pstore.  Only useful if you have
+	   a platform level driver that registers with pstore to
+	   provide the data, so you probably should just go say "Y"
+	   (or "M") to a platform specific persistent store driver
+	   (e.g. ACPI_APEI on X86) which will select this for you.
+	   If you don't have a platform persistent store driver,
+	   say N.

fs/pstore/Makefile

@@ -0,0 +1,7 @@
+#
+# Makefile for the linux pstorefs routines.
+#
+
+obj-y += pstore.o
+
+pstore-objs += inode.o platform.o

fs/pstore/inode.c

@@ -0,0 +1,280 @@
+/*
+ * Persistent Storage - ramfs parts.
+ *
+ * Copyright (C) 2010 Intel Corporation <[email protected]>
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License version 2 as
+ *  published by the Free Software Foundation.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program; if not, write to the Free Software
+ *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#include <linux/module.h>
+#include <linux/fs.h>
+#include <linux/fsnotify.h>
+#include <linux/pagemap.h>
+#include <linux/highmem.h>
+#include <linux/time.h>
+#include <linux/init.h>
+#include <linux/string.h>
+#include <linux/mount.h>
+#include <linux/ramfs.h>
+#include <linux/sched.h>
+#include <linux/magic.h>
+#include <linux/pstore.h>
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+
+#include "internal.h"
+
+#define	PSTORE_NAMELEN	64
+
+struct pstore_private {
+	u64	id;
+	int	(*erase)(u64);
+};
+
+#define pstore_get_inode ramfs_get_inode
+
+/*
+ * When a file is unlinked from our file system we call the
+ * platform driver to erase the record from persistent store.
+ */
+static int pstore_unlink(struct inode *dir, struct dentry *dentry)
+{
+	struct pstore_private *p = dentry->d_inode->i_private;
+
+	p->erase(p->id);
+	kfree(p);
+
+	return simple_unlink(dir, dentry);
+}
+
+static const struct inode_operations pstore_dir_inode_operations = {
+	.lookup		= simple_lookup,
+	.unlink		= pstore_unlink,
+};
+
+static const struct super_operations pstore_ops = {
+	.statfs		= simple_statfs,
+	.drop_inode	= generic_delete_inode,
+	.show_options	= generic_show_options,
+};
+
+static struct super_block *pstore_sb;
+static struct vfsmount *pstore_mnt;
+
+int pstore_is_mounted(void)
+{
+	return pstore_mnt != NULL;
+}
+
+/*
+ * Set up a file structure as if we had opened this file and
+ * write our data to it.
+ */
+static int pstore_writefile(struct inode *inode, struct dentry *dentry,
+	char *data, size_t size)
+{
+	struct file f;
+	ssize_t n;
+	mm_segment_t old_fs = get_fs();
+
+	memset(&f, '0', sizeof f);
+	f.f_mapping = inode->i_mapping;
+	f.f_path.dentry = dentry;
+	f.f_path.mnt = pstore_mnt;
+	f.f_pos = 0;
+	f.f_op = inode->i_fop;
+	set_fs(KERNEL_DS);
+	n = do_sync_write(&f, data, size, &f.f_pos);
+	set_fs(old_fs);
+
+	fsnotify_modify(&f);
+
+	return n == size;
+}
+
+/*
+ * Make a regular file in the root directory of our file system.
+ * Load it up with "size" bytes of data from "buf".
+ * Set the mtime & ctime to the date that this record was originally stored.
+ */
+int pstore_mkfile(enum pstore_type_id type, char *psname, u64 id,
+			      char *data, size_t size,
+			      struct timespec time, int (*erase)(u64))
+{
+	struct dentry		*root = pstore_sb->s_root;
+	struct dentry		*dentry;
+	struct inode		*inode;
+	int			rc;
+	char			name[PSTORE_NAMELEN];
+	struct pstore_private	*private;
+
+	rc = -ENOMEM;
+	inode = pstore_get_inode(pstore_sb, root->d_inode, S_IFREG | 0444, 0);
+	if (!inode)
+		goto fail;
+	inode->i_uid = inode->i_gid = 0;
+	private = kmalloc(sizeof *private, GFP_KERNEL);
+	if (!private)
+		goto fail_alloc;
+	private->id = id;
+	private->erase = erase;
+
+	switch (type) {
+	case PSTORE_TYPE_DMESG:
+		sprintf(name, "dmesg-%s-%lld", psname, id);
+		break;
+	case PSTORE_TYPE_MCE:
+		sprintf(name, "mce-%s-%lld", psname, id);
+		break;
+	case PSTORE_TYPE_UNKNOWN:
+		sprintf(name, "unknown-%s-%lld", psname, id);
+		break;
+	default:
+		sprintf(name, "type%d-%s-%lld", type, psname, id);
+		break;
+	}
+
+	mutex_lock(&root->d_inode->i_mutex);
+
+	rc = -ENOSPC;
+	dentry = d_alloc_name(root, name);
+	if (IS_ERR(dentry))
+		goto fail_lockedalloc;
+
+	d_add(dentry, inode);
+
+	mutex_unlock(&root->d_inode->i_mutex);
+
+	if (!pstore_writefile(inode, dentry, data, size))
+		goto fail_write;
+
+	inode->i_private = private;
+
+	if (time.tv_sec)
+		inode->i_mtime = inode->i_ctime = time;
+
+	return 0;
+
+fail_write:
+	kfree(private);
+	inode->i_nlink--;
+	mutex_lock(&root->d_inode->i_mutex);
+	d_delete(dentry);
+	dput(dentry);
+	mutex_unlock(&root->d_inode->i_mutex);
+	goto fail;
+
+fail_lockedalloc:
+	mutex_unlock(&root->d_inode->i_mutex);
+	kfree(private);
+fail_alloc:
+	iput(inode);
+
+fail:
+	return rc;
+}
+
+int pstore_fill_super(struct super_block *sb, void *data, int silent)
+{
+	struct inode *inode = NULL;
+	struct dentry *root;
+	int err;
+
+	save_mount_options(sb, data);
+
+	pstore_sb = sb;
+
+	sb->s_maxbytes		= MAX_LFS_FILESIZE;
+	sb->s_blocksize		= PAGE_CACHE_SIZE;
+	sb->s_blocksize_bits	= PAGE_CACHE_SHIFT;
+	sb->s_magic		= PSTOREFS_MAGIC;
+	sb->s_op		= &pstore_ops;
+	sb->s_time_gran		= 1;
+
+	inode = pstore_get_inode(sb, NULL, S_IFDIR | 0755, 0);
+	if (!inode) {
+		err = -ENOMEM;
+		goto fail;
+	}
+	/* override ramfs "dir" options so we catch unlink(2) */
+	inode->i_op = &pstore_dir_inode_operations;
+
+	root = d_alloc_root(inode);
+	sb->s_root = root;
+	if (!root) {
+		err = -ENOMEM;
+		goto fail;
+	}
+
+	pstore_get_records();
+
+	return 0;
+fail:
+	iput(inode);
+	return err;
+}
+
+static int pstore_get_sb(struct file_system_type *fs_type,
+	int flags, const char *dev_name, void *data, struct vfsmount *mnt)
+{
+	struct dentry *root;
+
+	root = mount_nodev(fs_type, flags, data, pstore_fill_super);
+	if (IS_ERR(root))
+		return -ENOMEM;
+
+	mnt->mnt_root = root;
+	mnt->mnt_sb = root->d_sb;
+	pstore_mnt = mnt;
+
+	return 0;
+}
+
+static void pstore_kill_sb(struct super_block *sb)
+{
+	kill_litter_super(sb);
+	pstore_sb = NULL;
+	pstore_mnt = NULL;
+}
+
+static struct file_system_type pstore_fs_type = {
+	.name		= "pstore",
+	.get_sb		= pstore_get_sb,
+	.kill_sb	= pstore_kill_sb,
+};
+
+static int __init init_pstore_fs(void)
+{
+	int ret = 0;
+	struct kobject *pstorefs_kobj;
+
+	pstorefs_kobj = kobject_create_and_add("pstore", fs_kobj);
+	if (!pstorefs_kobj)
+		return -ENOMEM;
+
+	sysfs_create_file(pstorefs_kobj, &pstore_kmsg_bytes_attr.attr);
+
+	ret = register_filesystem(&pstore_fs_type);
+
+	if (ret) {
+		sysfs_remove_file(pstorefs_kobj, &pstore_kmsg_bytes_attr.attr);
+		kobject_put(pstorefs_kobj);
+	}
+
+	return ret;
+}
+module_init(init_pstore_fs)
+
+MODULE_AUTHOR("Tony Luck <[email protected]>");
+MODULE_LICENSE("GPL");

fs/pstore/internal.h

@@ -0,0 +1,7 @@
+extern void	pstore_get_records(void);
+extern int	pstore_mkfile(enum pstore_type_id, char *psname, u64 id,
+			      char *data, size_t size,
+			      struct timespec time, int (*erase)(u64));
+extern int	pstore_is_mounted(void);
+
+extern struct kobj_attribute pstore_kmsg_bytes_attr;