Message-Id: <905DA1CC-63F8-4020-A1D7-1F59ABDF3448@dilger.ca>
Date:   Fri, 18 May 2018 13:05:20 -0600
From:   Andreas Dilger <adilger@...ger.ca>
To:     Kent Overstreet <kent.overstreet@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Chinner <dchinner@...hat.com>, darrick.wong@...cle.com,
        tytso@....edu, linux-btrfs@...r.kernel.org, clm@...com,
        jbacik@...com, viro@...iv.linux.org.uk, willy@...radead.org,
        peterz@...radead.org
Subject: Re: [PATCH 10/10] Dynamic fault injection

On May 18, 2018, at 1:49 AM, Kent Overstreet <kent.overstreet@...il.com> wrote:
> 
> Signed-off-by: Kent Overstreet <kent.overstreet@...il.com>

I agree with Christoph that even if there was some explanation in the cover
letter, there should be something at least as good in the patch itself.  The
cover letter is not saved, but the commit stays around forever, and should
explain how this should be added to code, and how to use it from userspace.


That said, I think this is a useful functionality.  We have something similar
in Lustre (OBD_FAIL_CHECK() and friends) that is necessary for being able to
test a distributed filesystem, which is just a CPP macro with an unlikely()
branch, while this looks more sophisticated.  This looks like it has some
added functionality like having more than one fault enabled at a time.
If this lands we could likely switch our code over to using this.


Some things that are missing from this patch that is in our code:

- in addition to the basic "enabled" and "oneshot" mechanisms, we have:
  - timeout: sleep for N msec to simulate network/disk/locking delays
  - race: wait with one thread until a second thread hits matching check

We also have a "fail_val" that allows making the check conditional (e.g.
only operation on server "N" should fail, only RPC opcode "N", etc).

Cheers, Andreas

> ---
> 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@...gle.com>
> + * Based on dynamic_debug.c:
> + * Copyright (C) 2008 Jason Baron <jbaron@...hat.com>
> + * By Greg Banks <gnb@...bourne.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
> 


Cheers, Andreas






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