[RFC] persistent store (version 3) (part 1 of 2)

[Luck, Tony]

Generic code for a "persistent store" file system as an interface
to provide a friendly user level ABI to platform specific drivers
for that access to some form of non-volatile storage that can be
used to save the dying words of an OS instance and make them
available after the reset/reboot.

Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>

---

Part 2 (smaller Cc: list) has the changes to the X86 ACPI/APEI/ERST
code that makes use of this.

Version 3 drops use of /sys and the "daft" "erase" file that is used
to clear entries from the persistent store. This version uses the much
more natural "rm file" to delete entries from the platform store. This
code is based on fs/ramfs - with most operations removed (cannot make
new files, directories, symlinks, hook for unlink to pass the erase
command down to the platform layer.

The bit that I think needs most eyeballs is pstore_mkfile() where I push
the data from the persistent store into the file. I couldn't find any
examples where other kernel code does this to copy - so I made it up.
Questions I have:
1) Is "struct file" too big to be on the stack? I can change it to kmalloc() it.
2) Did I get all the bits I need to fake a write to the file?
3) Is this whole thinng OK, or is there a better way? Peter had suggested
   that I use aops->write_begin() & aops->write_end(). But I got lost in
   the fs/vm code calling sequence working out what I'd need to set up
   before calling these - using do_sync_write() seemed a lot easier, but
   I've learned that "easy" is quite often not "right" :-)

Here's what the user sees now:

# ls -l /dev/pstore
total 16
-r--r--r--  1 root root 7896 Dec  3 10:56 dmesg-erst-5546531799825383425
# grep RIP: /dev/pstore/dmesg-erst-5546531799825383425
<4>[  552.268202] RIP: 0010:[<ffffffff812a3a25>]  [<ffffffff812a3a25>] sysrq_handle_crash+0x16/0x20
# rm /dev//pstore/dmesg-erst-5546531799825383425


diff --git a/Documentation/ABI/testing/pstore b/Documentation/ABI/testing/pstore
new file mode 100644
index 0000000..717fddb
--- /dev/null
+++ b/Documentation/ABI/testing/pstore
@@ -0,0 +1,35 @@
+Where:		/dev/pstore/...
+Date:		January 2011
+Kernel Version: 2.6.38
+Contact:	tony.luck@xxxxxxxxx
+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.
diff --git a/fs/Kconfig b/fs/Kconfig
index 771f457..2bbe47f 100644
--- a/fs/Kconfig
+++ b/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"
diff --git a/fs/Makefile b/fs/Makefile
index a7f7cef..db71a5b 100644
--- a/fs/Makefile
+++ b/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/
diff --git a/fs/pstore/Kconfig b/fs/pstore/Kconfig
new file mode 100644
index 0000000..867d0ac
--- /dev/null
+++ b/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.
diff --git a/fs/pstore/Makefile b/fs/pstore/Makefile
new file mode 100644
index 0000000..760f4bc
--- /dev/null
+++ b/fs/pstore/Makefile
@@ -0,0 +1,7 @@
+#
+# Makefile for the linux pstorefs routines.
+#
+
+obj-y += pstore.o
+
+pstore-objs += inode.o platform.o
diff --git a/fs/pstore/inode.c b/fs/pstore/inode.c
new file mode 100644
index 0000000..5673b83
--- /dev/null
+++ b/fs/pstore/inode.c
@@ -0,0 +1,185 @@
+/*
+ * Persistent Storage - ramfs parts.
+ *
+ * Copyright (C) 2010 Intel Corporation <tony.luck@xxxxxxxxx>
+ *
+ *  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/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/slab.h>
+#include <linux/uaccess.h>
+
+#include "internal.h"
+
+#define pstore_get_inode ramfs_get_inode
+
+static int pstore_unlink(struct inode *dir, struct dentry *dentry)
+{
+	pstore_erase(dentry->d_inode->i_private);
+
+	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;
+}
+
+/*
+ * 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(char *name, char *data, size_t size, struct timespec time,
+		  void *private)
+{
+	struct dentry *root = pstore_sb->s_root;
+	struct dentry *dentry;
+	struct inode *inode;
+	struct file f;
+	ssize_t n;
+	mm_segment_t old_fs = get_fs();
+
+	inode = pstore_get_inode(pstore_sb, root->d_inode, S_IFREG | 0444, 0);
+	if (!inode)
+		return -ENOMEM;
+
+	mutex_lock(&root->d_inode->i_mutex);
+
+	inode->i_private = private;
+
+	dentry = d_alloc_name(root, name);
+	if (!IS_ERR(dentry))
+		d_add(dentry, inode);
+
+	mutex_unlock(&root->d_inode->i_mutex);
+
+	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);
+
+	if (time.tv_sec)
+		inode->i_mtime = inode->i_ctime = time;
+
+	return (n == size) ? 0 : -EIO;
+}
+
+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)
+{
+	return register_filesystem(&pstore_fs_type);
+}
+module_init(init_pstore_fs)
+
+MODULE_AUTHOR("Tony Luck <tony.luck@xxxxxxxxx>");
+MODULE_LICENSE("GPL");
diff --git a/fs/pstore/internal.h b/fs/pstore/internal.h
new file mode 100644
index 0000000..1f274ff
--- /dev/null
+++ b/fs/pstore/internal.h
@@ -0,0 +1,5 @@
+extern void	pstore_get_records(void);
+extern int	pstore_mkfile(char *name, char *data, size_t size,
+			      struct timespec time, void *private);
+extern void	pstore_erase(void *private);
+extern int	pstore_is_mounted(void);
diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
new file mode 100644
index 0000000..63f08db
--- /dev/null
+++ b/fs/pstore/platform.c
@@ -0,0 +1,194 @@
+/*
+ * Persistent Storage - platform driver interface parts.
+ *
+ * Copyright (C) 2010 Intel Corporation <tony.luck@xxxxxxxxx>
+ *
+ *  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/atomic.h>
+#include <linux/types.h>
+#include <linux/errno.h>
+#include <linux/init.h>
+#include <linux/kmsg_dump.h>
+#include <linux/module.h>
+#include <linux/pstore.h>
+#include <linux/string.h>
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+
+#include "internal.h"
+
+/*
+ * pstore_lock just protects "psinfo" during
+ * calls to pstore_register()
+ */
+static DEFINE_SPINLOCK(pstore_lock);
+static struct pstore_info *psinfo;
+
+#define	PSTORE_NAMELEN	64
+
+struct pstore_private {
+	u64	id;
+	int	(*erase)(u64);
+};
+
+/*
+ * callback from kmsg_dump. (s2,l2) has the most recently
+ * written bytes, older bytes are in (s1,l1). Save as much
+ * as we can from the end of the buffer.
+ */
+static void pstore_dump(struct kmsg_dumper *dumper,
+	    enum kmsg_dump_reason reason,
+	    const char *s1, unsigned long l1,
+	    const char *s2, unsigned long l2)
+{
+	unsigned long s1_start, s2_start;
+	unsigned long l1_cpy, l2_cpy;
+	char *dst = psinfo->buf;
+
+	/* Don't dump oopses to persistent store */
+	if (reason == KMSG_DUMP_OOPS)
+		return;
+
+	l2_cpy = min(l2, psinfo->bufsize);
+	l1_cpy = min(l1, psinfo->bufsize - l2_cpy);
+
+	s2_start = l2 - l2_cpy;
+	s1_start = l1 - l1_cpy;
+
+	mutex_lock(&psinfo->mutex);
+	memcpy(dst, s1 + s1_start, l1_cpy);
+	memcpy(dst + l1_cpy, s2 + s2_start, l2_cpy);
+
+	psinfo->write(PSTORE_TYPE_DMESG, l1_cpy + l2_cpy);
+	mutex_unlock(&psinfo->mutex);
+}
+
+static struct kmsg_dumper pstore_dumper = {
+	.dump = pstore_dump,
+};
+
+/*
+ * platform specific persistent storage driver registers with
+ * us here. If pstore is already mounted, call the platform
+ * read function right away to populate the file system. If not
+ * then the pstore mount code will call us later to fill out
+ * the file system.
+ *
+ * Register with kmsg_dump to save last part of console log on panic.
+ */
+int pstore_register(struct pstore_info *psi)
+{
+	struct module *owner = psi->owner;
+
+	spin_lock(&pstore_lock);
+	if (psinfo) {
+		spin_unlock(&pstore_lock);
+		return -EBUSY;
+	}
+	psinfo = psi;
+	spin_unlock(&pstore_lock);
+
+	if (owner && !try_module_get(owner)) {
+		psinfo = NULL;
+		return -EINVAL;
+	}
+
+	if (pstore_is_mounted())
+		pstore_get_records();
+
+	kmsg_dump_register(&pstore_dumper);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(pstore_register);
+
+/*
+ * Read all the records from the persistent store. Create and
+ * file files in our filesystem.
+ */
+void pstore_get_records(void)
+{
+	struct pstore_info *psi = psinfo;
+	size_t			size;
+	u64			id;
+	int			type;
+	char			name[PSTORE_NAMELEN];
+	struct pstore_private	*private;
+	struct timespec		time;
+
+	if (!psi)
+		return;
+
+	mutex_lock(&psinfo->mutex);
+	for (;;) {
+		if (psi->read(&id, &type, &size, &time) <= 0)
+			break;
+		switch (type) {
+		case PSTORE_TYPE_DMESG:
+			sprintf(name, "dmesg-%s-%lld", psi->name, id);
+			break;
+		case PSTORE_TYPE_MCE:
+			sprintf(name, "mce-%s-%lld", psi->name, id);
+			break;
+		default:
+			sprintf(name, "type%d-%s-%lld", type, psi->name, id);
+			break;
+		}
+		private = kmalloc(sizeof *private, GFP_KERNEL);
+		private->id = id;
+		private->erase = psi->erase;
+		pstore_mkfile(name, psi->buf, size, time, private);
+	}
+	mutex_unlock(&psinfo->mutex);
+}
+
+/*
+ * Call platform driver to write a record to the
+ * persistent store. We don't worry about making
+ * this visible in the pstore filesystem as the
+ * presumption is that we only save things to the
+ * store in the dying moments of OS failure. Hence
+ * nobody will see the entries in the filesystem.
+ */
+int pstore_write(int type, char *buf, size_t size)
+{
+	int	ret;
+
+	if (!psinfo)
+		return -ENODEV;
+	if (size > psinfo->bufsize)
+		return -EFBIG;
+
+	mutex_lock(&psinfo->mutex);
+	memcpy(psinfo->buf, buf, size);
+	ret = psinfo->write(type, size);
+	mutex_unlock(&psinfo->mutex);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(pstore_write);
+
+/*
+ * When a file is unlinked from our file system we call the
+ * platform driver to erase the record from persistent store.
+ */
+void pstore_erase(void *private)
+{
+	struct pstore_private *p = private;
+
+	p->erase(p->id);
+	kfree(p);
+}
diff --git a/include/linux/magic.h b/include/linux/magic.h
index ff690d0..e87fd5a 100644
--- a/include/linux/magic.h
+++ b/include/linux/magic.h
@@ -26,6 +26,7 @@
 #define ISOFS_SUPER_MAGIC	0x9660
 #define JFFS2_SUPER_MAGIC	0x72b6
 #define ANON_INODE_FS_MAGIC	0x09041934
+#define PSTOREFS_MAGIC		0x6165676C
 
 #define MINIX_SUPER_MAGIC	0x137F		/* original minix fs */
 #define MINIX_SUPER_MAGIC2	0x138F		/* minix fs, 30 char names */
diff --git a/include/linux/pstore.h b/include/linux/pstore.h
new file mode 100644
index 0000000..4d635c0
--- /dev/null
+++ b/include/linux/pstore.h
@@ -0,0 +1,57 @@
+/*
+ * Persistent Storage - pstore.h
+ *
+ * Copyright (C) 2010 Intel Corporation <tony.luck@xxxxxxxxx>
+ *
+ * This code is the generic layer to export data records from platform
+ * level persistent storage via a file system.
+ *
+ *  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
+ */
+#ifndef _LINUX_PSTORE_H
+#define _LINUX_PSTORE_H
+
+/* types */
+#define	PSTORE_TYPE_DMESG	0
+#define	PSTORE_TYPE_MCE		1
+
+struct pstore_info {
+	struct module	*owner;
+	char		*name;
+	struct mutex	mutex;	/* serialize access to 'buf' */
+	char		*buf;
+	size_t		bufsize;
+	int		(*read)(u64 *id, int *type, size_t *size,
+			struct timespec *time);
+	int		(*write)(int type, size_t size);
+	int		(*erase)(u64 id);
+};
+
+#if defined(CONFIG_PSTORE) || defined(CONFIG_PSTORE_MODULE)
+extern int pstore_register(struct pstore_info *);
+extern int pstore_write(int type, char *buf, size_t size);
+#else
+static inline int
+pstore_register(struct pstore_info *psi)
+{
+	return -ENODEV;
+}
+static inline int
+pstore_write(int type, char *buf, size_t size)
+{
+	return -ENODEV;
+}
+#endif
+
+#endif /*_LINUX_PSTORE_H*/
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