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From:   Kent Overstreet <kent.overstreet@gmail.com>
To:     linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Cc:     Kent Overstreet <kent.overstreet@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Dave Chinner <dchinner@redhat.com>, darrick.wong@oracle.com,
        tytso@mit.edu, linux-btrfs@vger.kernel.org, clm@fb.com,
        jbacik@fb.com, viro@zeniv.linux.org.uk, willy@infradead.org,
        peterz@infradead.org
Subject: [PATCH 10/10] Dynamic fault injection
Date:   Fri, 18 May 2018 03:49:18 -0400
Message-Id: <20180518074918.13816-21-kent.overstreet@gmail.com>
In-Reply-To: <20180518074918.13816-1-kent.overstreet@gmail.com>
References: <20180518074918.13816-1-kent.overstreet@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
---
 include/asm-generic/vmlinux.lds.h |   4 +
 include/linux/dynamic_fault.h     | 117 +++++
 lib/Kconfig.debug                 |   5 +
 lib/Makefile                      |   2 +
 lib/dynamic_fault.c               | 760 ++++++++++++++++++++++++++++++
 5 files changed, 888 insertions(+)
 create mode 100644 include/linux/dynamic_fault.h
 create mode 100644 lib/dynamic_fault.c

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 1ab0e520d6..a4c9dfcbbd 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -246,6 +246,10 @@
 	VMLINUX_SYMBOL(__start___verbose) = .;                          \
 	KEEP(*(__verbose))                                              \
 	VMLINUX_SYMBOL(__stop___verbose) = .;				\
+	. = ALIGN(8);							\
+	VMLINUX_SYMBOL(__start___faults) = .;                           \
+	*(__faults)                                                     \
+	VMLINUX_SYMBOL(__stop___faults) = .;				\
 	LIKELY_PROFILE()		       				\
 	BRANCH_PROFILE()						\
 	TRACE_PRINTKS()							\
diff --git a/include/linux/dynamic_fault.h b/include/linux/dynamic_fault.h
new file mode 100644
index 0000000000..6e7bb56ae8
--- /dev/null
+++ b/include/linux/dynamic_fault.h
@@ -0,0 +1,117 @@
+#ifndef _DYNAMIC_FAULT_H
+#define _DYNAMIC_FAULT_H
+
+#include <linux/bio.h>
+#include <linux/jump_label.h>
+#include <linux/slab.h>
+
+enum dfault_enabled {
+	DFAULT_DISABLED,
+	DFAULT_ENABLED,
+	DFAULT_ONESHOT,
+};
+
+union dfault_state {
+	struct {
+		unsigned		enabled:2;
+		unsigned		count:30;
+	};
+
+	struct {
+		unsigned		v;
+	};
+};
+
+/*
+ * An instance of this structure is created in a special
+ * ELF section at every dynamic fault callsite.  At runtime,
+ * the special section is treated as an array of these.
+ */
+struct _dfault {
+	const char		*modname;
+	const char		*function;
+	const char		*filename;
+	const char		*class;
+
+	const u16		line;
+
+	unsigned		frequency;
+	union dfault_state	state;
+
+	struct static_key	enabled;
+} __aligned(8);
+
+
+#ifdef CONFIG_DYNAMIC_FAULT
+
+int dfault_add_module(struct _dfault *tab, unsigned int n, const char *mod);
+int dfault_remove_module(char *mod_name);
+bool __dynamic_fault_enabled(struct _dfault *);
+
+#define dynamic_fault(_class)						\
+({									\
+	static struct _dfault descriptor				\
+	__used __aligned(8) __attribute__((section("__faults"))) = {	\
+		.modname	= KBUILD_MODNAME,			\
+		.function	= __func__,				\
+		.filename	= __FILE__,				\
+		.line		= __LINE__,				\
+		.class		= _class,				\
+	};								\
+									\
+	static_key_false(&descriptor.enabled) &&			\
+		__dynamic_fault_enabled(&descriptor);			\
+})
+
+#define memory_fault()		dynamic_fault("memory")
+#define race_fault()		dynamic_fault("race")
+
+#define kmalloc(...)							\
+	(memory_fault() ? NULL	: kmalloc(__VA_ARGS__))
+#define kzalloc(...)							\
+	(memory_fault() ? NULL	: kzalloc(__VA_ARGS__))
+#define krealloc(...)							\
+	(memory_fault() ? NULL	: krealloc(__VA_ARGS__))
+
+#define mempool_alloc(pool, gfp_mask)					\
+	((!gfpflags_allow_blocking(gfp_mask) && memory_fault())		\
+		? NULL : mempool_alloc(pool, gfp_mask))
+
+#define __get_free_pages(...)						\
+	(memory_fault() ? 0	: __get_free_pages(__VA_ARGS__))
+#define alloc_pages_node(...)						\
+	(memory_fault() ? NULL	: alloc_pages_node(__VA_ARGS__))
+#define alloc_pages_nodemask(...)					\
+	(memory_fault() ? NULL	: alloc_pages_nodemask(__VA_ARGS__))
+
+#define bio_alloc_bioset(gfp_mask, ...)					\
+	((!gfpflags_allow_blocking(gfp_mask) && memory_fault())		\
+	 ? NULL	: bio_alloc_bioset(gfp_mask, __VA_ARGS__))
+
+#define bio_clone(bio, gfp_mask)					\
+	((!gfpflags_allow_blocking(gfp_mask) && memory_fault())		\
+	 ? NULL	: bio_clone(bio, gfp_mask))
+
+#define bio_clone_bioset(bio, gfp_mask, bs)				\
+	((!gfpflags_allow_blocking(gfp_mask) && memory_fault())		\
+	 ? NULL	: bio_clone_bioset(bio, gfp_mask, bs))
+
+#define bio_kmalloc(...)						\
+	(memory_fault() ? NULL		: bio_kmalloc(__VA_ARGS__))
+#define bio_clone_kmalloc(...)						\
+	(memory_fault() ? NULL		: bio_clone_kmalloc(__VA_ARGS__))
+
+#define bio_iov_iter_get_pages(...)					\
+	(memory_fault() ? -ENOMEM	: bio_iov_iter_get_pages(__VA_ARGS__))
+
+#else /* CONFIG_DYNAMIC_FAULT */
+
+#define dfault_add_module(tab, n, modname)	0
+#define dfault_remove_module(mod)		0
+#define dynamic_fault(_class)			0
+#define memory_fault()				0
+#define race_fault()				0
+
+#endif /* CONFIG_DYNAMIC_FAULT */
+
+#endif
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 427292a759..7b7ca0d813 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1599,6 +1599,11 @@ config LATENCYTOP
 	  Enable this option if you want to use the LatencyTOP tool
 	  to find out which userspace is blocking on what kernel operations.
 
+config DYNAMIC_FAULT
+	bool "Enable dynamic fault support"
+	default n
+	depends on DEBUG_FS
+
 source kernel/trace/Kconfig
 
 config PROVIDE_OHCI1394_DMA_INIT
diff --git a/lib/Makefile b/lib/Makefile
index 66d2231d70..f6f70f4771 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -158,6 +158,8 @@ obj-$(CONFIG_HAVE_ARCH_TRACEHOOK) += syscall.o
 
 obj-$(CONFIG_DYNAMIC_DEBUG) += dynamic_debug.o
 
+obj-$(CONFIG_DYNAMIC_FAULT) += dynamic_fault.o
+
 obj-$(CONFIG_NLATTR) += nlattr.o
 
 obj-$(CONFIG_LRU_CACHE) += lru_cache.o
diff --git a/lib/dynamic_fault.c b/lib/dynamic_fault.c
new file mode 100644
index 0000000000..75fc9a1b4b
--- /dev/null
+++ b/lib/dynamic_fault.c
@@ -0,0 +1,760 @@
+/*
+ * lib/dynamic_fault.c
+ *
+ * make dynamic_fault() calls runtime configurable based upon their
+ * source module.
+ *
+ * Copyright (C) 2011 Adam Berkan <aberkan@google.com>
+ * Based on dynamic_debug.c:
+ * Copyright (C) 2008 Jason Baron <jbaron@redhat.com>
+ * By Greg Banks <gnb@melbourne.sgi.com>
+ * Copyright (c) 2008 Silicon Graphics Inc.  All Rights Reserved.
+ *
+ */
+
+#define pr_fmt(fmt) "dfault: " fmt "\n"
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/kallsyms.h>
+#include <linux/version.h>
+#include <linux/types.h>
+#include <linux/mutex.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+#include <linux/list.h>
+#include <linux/sysctl.h>
+#include <linux/ctype.h>
+#include <linux/string.h>
+#include <linux/uaccess.h>
+#include <linux/dynamic_fault.h>
+#include <linux/debugfs.h>
+#include <linux/slab.h>
+
+#undef kzalloc
+
+extern struct _dfault __start___faults[];
+extern struct _dfault __stop___faults[];
+
+struct dfault_table {
+	struct list_head link;
+	char *mod_name;
+	unsigned int num_dfaults;
+	struct _dfault *dfaults;
+};
+
+struct dfault_query {
+	const char	*filename;
+	const char	*module;
+	const char	*function;
+	const char	*class;
+	unsigned int	first_line, last_line;
+	unsigned int	first_index, last_index;
+
+	unsigned	match_line:1;
+	unsigned	match_index:1;
+
+	unsigned	set_enabled:1;
+	unsigned	enabled:2;
+
+	unsigned	set_frequency:1;
+	unsigned	frequency;
+};
+
+struct dfault_iter {
+	struct dfault_table *table;
+	unsigned int idx;
+};
+
+static DEFINE_MUTEX(dfault_lock);
+static LIST_HEAD(dfault_tables);
+
+bool __dynamic_fault_enabled(struct _dfault *df)
+{
+	union dfault_state old, new;
+	unsigned v = df->state.v;
+	bool ret;
+
+	do {
+		old.v = new.v = v;
+
+		if (new.enabled == DFAULT_DISABLED)
+			return false;
+
+		ret = df->frequency
+			? ++new.count >= df->frequency
+			: true;
+		if (ret)
+			new.count = 0;
+		if (ret && new.enabled == DFAULT_ONESHOT)
+			new.enabled = DFAULT_DISABLED;
+	} while ((v = cmpxchg(&df->state.v, old.v, new.v)) != old.v);
+
+	if (ret)
+		pr_debug("returned true for %s:%u", df->filename, df->line);
+
+	return ret;
+}
+EXPORT_SYMBOL(__dynamic_fault_enabled);
+
+/* Return the last part of a pathname */
+static inline const char *basename(const char *path)
+{
+	const char *tail = strrchr(path, '/');
+
+	return tail ? tail + 1 : path;
+}
+
+/* format a string into buf[] which describes the _dfault's flags */
+static char *dfault_describe_flags(struct _dfault *df, char *buf, size_t buflen)
+{
+	switch (df->state.enabled) {
+	case DFAULT_DISABLED:
+		strlcpy(buf, "disabled", buflen);
+		break;
+	case DFAULT_ENABLED:
+		strlcpy(buf, "enabled", buflen);
+		break;
+	case DFAULT_ONESHOT:
+		strlcpy(buf, "oneshot", buflen);
+		break;
+	default:
+		BUG();
+	}
+
+	return buf;
+}
+
+/*
+ * must be called with dfault_lock held
+ */
+
+/*
+ * Search the tables for _dfault's which match the given
+ * `query' and apply the `flags' and `mask' to them.  Tells
+ * the user which dfault's were changed, or whether none
+ * were matched.
+ */
+static int dfault_change(const struct dfault_query *query)
+{
+	struct dfault_table *dt;
+	unsigned int nfound = 0;
+	unsigned i, index = 0;
+	char flagbuf[16];
+
+	/* search for matching dfaults */
+	mutex_lock(&dfault_lock);
+	list_for_each_entry(dt, &dfault_tables, link) {
+
+		/* match against the module name */
+		if (query->module != NULL &&
+		    strcmp(query->module, dt->mod_name))
+			continue;
+
+		for (i = 0 ; i < dt->num_dfaults ; i++) {
+			struct _dfault *df = &dt->dfaults[i];
+
+			/* match against the source filename */
+			if (query->filename != NULL &&
+			    strcmp(query->filename, df->filename) &&
+			    strcmp(query->filename, basename(df->filename)))
+				continue;
+
+			/* match against the function */
+			if (query->function != NULL &&
+			    strcmp(query->function, df->function))
+				continue;
+
+			/* match against the class */
+			if (query->class) {
+				size_t len = strlen(query->class);
+
+				if (strncmp(query->class, df->class, len))
+					continue;
+
+				if (df->class[len] && df->class[len] != ':')
+					continue;
+			}
+
+			/* match against the line number range */
+			if (query->match_line &&
+			    (df->line < query->first_line ||
+			     df->line > query->last_line))
+				continue;
+
+			/* match against the fault index */
+			if (query->match_index &&
+			    (index < query->first_index ||
+			     index > query->last_index)) {
+				index++;
+				continue;
+			}
+
+			if (query->set_enabled &&
+			    query->enabled != df->state.enabled) {
+				if (query->enabled != DFAULT_DISABLED)
+					static_key_slow_inc(&df->enabled);
+				else if (df->state.enabled != DFAULT_DISABLED)
+					static_key_slow_dec(&df->enabled);
+
+				df->state.enabled = query->enabled;
+			}
+
+			if (query->set_frequency)
+				df->frequency = query->frequency;
+
+			pr_debug("changed %s:%d [%s]%s #%d %s",
+				 df->filename, df->line, dt->mod_name,
+				 df->function, index,
+				 dfault_describe_flags(df, flagbuf,
+						       sizeof(flagbuf)));
+
+			index++;
+			nfound++;
+		}
+	}
+	mutex_unlock(&dfault_lock);
+
+	pr_debug("dfault: %u matches", nfound);
+
+	return nfound ? 0 : -ENOENT;
+}
+
+/*
+ * Split the buffer `buf' into space-separated words.
+ * Handles simple " and ' quoting, i.e. without nested,
+ * embedded or escaped \".  Return the number of words
+ * or <0 on error.
+ */
+static int dfault_tokenize(char *buf, char *words[], int maxwords)
+{
+	int nwords = 0;
+
+	while (*buf) {
+		char *end;
+
+		/* Skip leading whitespace */
+		buf = skip_spaces(buf);
+		if (!*buf)
+			break;	/* oh, it was trailing whitespace */
+
+		/* Run `end' over a word, either whitespace separated or quoted
+		 */
+		if (*buf == '"' || *buf == '\'') {
+			int quote = *buf++;
+
+			for (end = buf ; *end && *end != quote ; end++)
+				;
+			if (!*end)
+				return -EINVAL;	/* unclosed quote */
+		} else {
+			for (end = buf ; *end && !isspace(*end) ; end++)
+				;
+			BUG_ON(end == buf);
+		}
+		/* Here `buf' is the start of the word, `end' is one past the
+		 * end
+		 */
+
+		if (nwords == maxwords)
+			return -EINVAL;	/* ran out of words[] before bytes */
+		if (*end)
+			*end++ = '\0';	/* terminate the word */
+		words[nwords++] = buf;
+		buf = end;
+	}
+
+	return nwords;
+}
+
+/*
+ * Parse a range.
+ */
+static inline int parse_range(char *str,
+			      unsigned int *first,
+			      unsigned int *last)
+{
+	char *first_str = str;
+	char *last_str = strchr(first_str, '-');
+
+	if (last_str)
+		*last_str++ = '\0';
+
+	if (kstrtouint(first_str, 10, first))
+		return -EINVAL;
+
+	if (!last_str)
+		*last = *first;
+	else if (kstrtouint(last_str, 10, last))
+		return -EINVAL;
+
+	return 0;
+}
+
+enum dfault_token {
+	TOK_INVALID,
+
+	/* Queries */
+	TOK_FUNC,
+	TOK_FILE,
+	TOK_LINE,
+	TOK_MODULE,
+	TOK_CLASS,
+	TOK_INDEX,
+
+	/* Commands */
+	TOK_DISABLE,
+	TOK_ENABLE,
+	TOK_ONESHOT,
+	TOK_FREQUENCY,
+};
+
+static const struct {
+	const char		*str;
+	enum dfault_token	tok;
+	unsigned		args_required;
+} dfault_token_strs[] = {
+	{ "func",	TOK_FUNC,	1,	},
+	{ "file",	TOK_FILE,	1,	},
+	{ "line",	TOK_LINE,	1,	},
+	{ "module",	TOK_MODULE,	1,	},
+	{ "class",	TOK_CLASS,	1,	},
+	{ "index",	TOK_INDEX,	1,	},
+	{ "disable",	TOK_DISABLE,	0,	},
+	{ "enable",	TOK_ENABLE,	0,	},
+	{ "oneshot",	TOK_ONESHOT,	0,	},
+	{ "frequency",	TOK_FREQUENCY,	1,	},
+};
+
+static enum dfault_token str_to_token(const char *word, unsigned nr_words)
+{
+	unsigned i;
+
+	for (i = 0; i < ARRAY_SIZE(dfault_token_strs); i++)
+		if (!strcmp(word, dfault_token_strs[i].str)) {
+			if (nr_words < dfault_token_strs[i].args_required) {
+				pr_debug("insufficient arguments to \"%s\"",
+					 word);
+				return TOK_INVALID;
+			}
+
+			return dfault_token_strs[i].tok;
+		}
+
+	pr_debug("unknown keyword \"%s\"", word);
+
+	return TOK_INVALID;
+}
+
+static int dfault_parse_command(struct dfault_query *query,
+				enum dfault_token tok,
+				char *words[], size_t nr_words)
+{
+	unsigned i = 0;
+	int ret;
+
+	switch (tok) {
+	case TOK_INVALID:
+		return -EINVAL;
+	case TOK_FUNC:
+		query->function = words[i++];
+	case TOK_FILE:
+		query->filename = words[i++];
+		return 1;
+	case TOK_LINE:
+		ret = parse_range(words[i++],
+				  &query->first_line,
+				  &query->last_line);
+		if (ret)
+			return ret;
+		query->match_line = true;
+		break;
+	case TOK_MODULE:
+		query->module = words[i++];
+		break;
+	case TOK_CLASS:
+		query->class = words[i++];
+		break;
+	case TOK_INDEX:
+		ret = parse_range(words[i++],
+				  &query->first_index,
+				  &query->last_index);
+		if (ret)
+			return ret;
+		query->match_index = true;
+		break;
+	case TOK_DISABLE:
+		query->set_enabled = true;
+		query->enabled = DFAULT_DISABLED;
+		break;
+	case TOK_ENABLE:
+		query->set_enabled = true;
+		query->enabled = DFAULT_ENABLED;
+		break;
+	case TOK_ONESHOT:
+		query->set_enabled = true;
+		query->enabled = DFAULT_ONESHOT;
+		break;
+	case TOK_FREQUENCY:
+		query->set_frequency = 1;
+		ret = kstrtouint(words[i++], 10, &query->frequency);
+		if (ret)
+			return ret;
+
+		if (!query->set_enabled) {
+			query->set_enabled = 1;
+			query->enabled = DFAULT_ENABLED;
+		}
+		break;
+	}
+
+	return i;
+}
+
+/*
+ * Parse words[] as a dfault query specification, which is a series
+ * of (keyword, value) pairs chosen from these possibilities:
+ *
+ * func <function-name>
+ * file <full-pathname>
+ * file <base-filename>
+ * module <module-name>
+ * line <lineno>
+ * line <first-lineno>-<last-lineno> // where either may be empty
+ * index <m>-<n>                     // dynamic faults numbered from <m>
+ *                                   // to <n> inside each matching function
+ */
+static int dfault_parse_query(struct dfault_query *query,
+			      char *words[], size_t nr_words)
+{
+	unsigned i = 0;
+
+	while (i < nr_words) {
+		const char *tok_str = words[i++];
+		enum dfault_token tok = str_to_token(tok_str, nr_words - i);
+		int ret = dfault_parse_command(query, tok, words + i,
+					       nr_words - i);
+
+		if (ret < 0)
+			return ret;
+		i += ret;
+		BUG_ON(i > nr_words);
+	}
+
+	return 0;
+}
+
+/*
+ * File_ops->write method for <debugfs>/dynamic_fault/conrol.  Gathers the
+ * command text from userspace, parses and executes it.
+ */
+static ssize_t dfault_proc_write(struct file *file, const char __user *ubuf,
+				  size_t len, loff_t *offp)
+{
+	struct dfault_query query;
+#define MAXWORDS 9
+	int nwords;
+	char *words[MAXWORDS];
+	char tmpbuf[256];
+	int ret;
+
+	memset(&query, 0, sizeof(query));
+
+	if (len == 0)
+		return 0;
+	/* we don't check *offp -- multiple writes() are allowed */
+	if (len > sizeof(tmpbuf)-1)
+		return -E2BIG;
+	if (copy_from_user(tmpbuf, ubuf, len))
+		return -EFAULT;
+	tmpbuf[len] = '\0';
+
+	pr_debug("read %zu bytes from userspace", len);
+
+	nwords = dfault_tokenize(tmpbuf, words, MAXWORDS);
+	if (nwords < 0)
+		return -EINVAL;
+	if (dfault_parse_query(&query, words, nwords))
+		return -EINVAL;
+
+	/* actually go and implement the change */
+	ret = dfault_change(&query);
+	if (ret < 0)
+		return ret;
+
+	*offp += len;
+	return len;
+}
+
+/* Control file read code */
+
+/*
+ * Set the iterator to point to the first _dfault object
+ * and return a pointer to that first object.  Returns
+ * NULL if there are no _dfaults at all.
+ */
+static struct _dfault *dfault_iter_first(struct dfault_iter *iter)
+{
+	if (list_empty(&dfault_tables)) {
+		iter->table = NULL;
+		iter->idx = 0;
+		return NULL;
+	}
+	iter->table = list_entry(dfault_tables.next,
+				 struct dfault_table, link);
+	iter->idx = 0;
+	return &iter->table->dfaults[iter->idx];
+}
+
+/*
+ * Advance the iterator to point to the next _dfault
+ * object from the one the iterator currently points at,
+ * and returns a pointer to the new _dfault.  Returns
+ * NULL if the iterator has seen all the _dfaults.
+ */
+static struct _dfault *dfault_iter_next(struct dfault_iter *iter)
+{
+	if (iter->table == NULL)
+		return NULL;
+	if (++iter->idx == iter->table->num_dfaults) {
+		/* iterate to next table */
+		iter->idx = 0;
+		if (list_is_last(&iter->table->link, &dfault_tables)) {
+			iter->table = NULL;
+			return NULL;
+		}
+		iter->table = list_entry(iter->table->link.next,
+					 struct dfault_table, link);
+	}
+	return &iter->table->dfaults[iter->idx];
+}
+
+/*
+ * Seq_ops start method.  Called at the start of every
+ * read() call from userspace.  Takes the dfault_lock and
+ * seeks the seq_file's iterator to the given position.
+ */
+static void *dfault_proc_start(struct seq_file *m, loff_t *pos)
+{
+	struct dfault_iter *iter = m->private;
+	struct _dfault *dp;
+	int n = *pos;
+
+	mutex_lock(&dfault_lock);
+
+	if (n < 0)
+		return NULL;
+	dp = dfault_iter_first(iter);
+	while (dp != NULL && --n >= 0)
+		dp = dfault_iter_next(iter);
+	return dp;
+}
+
+/*
+ * Seq_ops next method.  Called several times within a read()
+ * call from userspace, with dfault_lock held.  Walks to the
+ * next _dfault object with a special case for the header line.
+ */
+static void *dfault_proc_next(struct seq_file *m, void *p, loff_t *pos)
+{
+	struct dfault_iter *iter = m->private;
+	struct _dfault *dp;
+
+	if (p == SEQ_START_TOKEN)
+		dp = dfault_iter_first(iter);
+	else
+		dp = dfault_iter_next(iter);
+	++*pos;
+	return dp;
+}
+
+/*
+ * Seq_ops show method.  Called several times within a read()
+ * call from userspace, with dfault_lock held.  Formats the
+ * current _dfault as a single human-readable line, with a
+ * special case for the header line.
+ */
+static int dfault_proc_show(struct seq_file *m, void *p)
+{
+	struct dfault_iter *iter = m->private;
+	struct _dfault *df = p;
+	char flagsbuf[8];
+
+	seq_printf(m, "%s:%u class:%s module:%s func:%s %s \"\"\n",
+		   df->filename, df->line, df->class,
+		   iter->table->mod_name, df->function,
+		   dfault_describe_flags(df, flagsbuf, sizeof(flagsbuf)));
+
+	return 0;
+}
+
+/*
+ * Seq_ops stop method.  Called at the end of each read()
+ * call from userspace.  Drops dfault_lock.
+ */
+static void dfault_proc_stop(struct seq_file *m, void *p)
+{
+	mutex_unlock(&dfault_lock);
+}
+
+static const struct seq_operations dfault_proc_seqops = {
+	.start = dfault_proc_start,
+	.next = dfault_proc_next,
+	.show = dfault_proc_show,
+	.stop = dfault_proc_stop
+};
+
+/*
+ * File_ops->open method for <debugfs>/dynamic_fault/control.  Does the seq_file
+ * setup dance, and also creates an iterator to walk the _dfaults.
+ * Note that we create a seq_file always, even for O_WRONLY files
+ * where it's not needed, as doing so simplifies the ->release method.
+ */
+static int dfault_proc_open(struct inode *inode, struct file *file)
+{
+	struct dfault_iter *iter;
+	int err;
+
+	iter = kzalloc(sizeof(*iter), GFP_KERNEL);
+	if (iter == NULL)
+		return -ENOMEM;
+
+	err = seq_open(file, &dfault_proc_seqops);
+	if (err) {
+		kfree(iter);
+		return err;
+	}
+	((struct seq_file *) file->private_data)->private = iter;
+	return 0;
+}
+
+static const struct file_operations dfault_proc_fops = {
+	.owner = THIS_MODULE,
+	.open = dfault_proc_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = seq_release_private,
+	.write = dfault_proc_write
+};
+
+/*
+ * Allocate a new dfault_table for the given module
+ * and add it to the global list.
+ */
+int dfault_add_module(struct _dfault *tab, unsigned int n,
+		      const char *name)
+{
+	struct dfault_table *dt;
+	char *new_name;
+	const char *func = NULL;
+	int i;
+
+	dt = kzalloc(sizeof(*dt), GFP_KERNEL);
+	if (dt == NULL)
+		return -ENOMEM;
+	new_name = kstrdup(name, GFP_KERNEL);
+	if (new_name == NULL) {
+		kfree(dt);
+		return -ENOMEM;
+	}
+	dt->mod_name = new_name;
+	dt->num_dfaults = n;
+	dt->dfaults = tab;
+
+	mutex_lock(&dfault_lock);
+	list_add_tail(&dt->link, &dfault_tables);
+	mutex_unlock(&dfault_lock);
+
+	/* __attribute__(("section")) emits things in reverse order */
+	for (i = n - 1; i >= 0; i--)
+		if (!func || strcmp(tab[i].function, func))
+			func = tab[i].function;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(dfault_add_module);
+
+static void dfault_table_free(struct dfault_table *dt)
+{
+	list_del_init(&dt->link);
+	kfree(dt->mod_name);
+	kfree(dt);
+}
+
+/*
+ * Called in response to a module being unloaded.  Removes
+ * any dfault_table's which point at the module.
+ */
+int dfault_remove_module(char *mod_name)
+{
+	struct dfault_table *dt, *nextdt;
+	int ret = -ENOENT;
+
+	mutex_lock(&dfault_lock);
+	list_for_each_entry_safe(dt, nextdt, &dfault_tables, link) {
+		if (!strcmp(dt->mod_name, mod_name)) {
+			dfault_table_free(dt);
+			ret = 0;
+		}
+	}
+	mutex_unlock(&dfault_lock);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(dfault_remove_module);
+
+static void dfault_remove_all_tables(void)
+{
+	mutex_lock(&dfault_lock);
+	while (!list_empty(&dfault_tables)) {
+		struct dfault_table *dt = list_entry(dfault_tables.next,
+						      struct dfault_table,
+						      link);
+		dfault_table_free(dt);
+	}
+	mutex_unlock(&dfault_lock);
+}
+
+static int __init dynamic_fault_init(void)
+{
+	struct dentry *dir, *file;
+	struct _dfault *iter, *iter_start;
+	const char *modname = NULL;
+	int ret = 0;
+	int n = 0;
+
+	dir = debugfs_create_dir("dynamic_fault", NULL);
+	if (!dir)
+		return -ENOMEM;
+	file = debugfs_create_file("control", 0644, dir, NULL,
+					&dfault_proc_fops);
+	if (!file) {
+		debugfs_remove(dir);
+		return -ENOMEM;
+	}
+	if (__start___faults != __stop___faults) {
+		iter = __start___faults;
+		modname = iter->modname;
+		iter_start = iter;
+		for (; iter < __stop___faults; iter++) {
+			if (strcmp(modname, iter->modname)) {
+				ret = dfault_add_module(iter_start, n, modname);
+				if (ret)
+					goto out_free;
+				n = 0;
+				modname = iter->modname;
+				iter_start = iter;
+			}
+			n++;
+		}
+		ret = dfault_add_module(iter_start, n, modname);
+	}
+out_free:
+	if (ret) {
+		dfault_remove_all_tables();
+		debugfs_remove(dir);
+		debugfs_remove(file);
+	}
+	return 0;
+}
+module_init(dynamic_fault_init);
-- 
2.17.0