[PATCH v3 0/2] Move BTRFS RCU string to common library

[PATCH v3 0/2] Move BTRFS RCU string to common library

[Omar Sandoval]

This patch series makes the generic RCU string library used internally by BTRFS
accessible by anyone.

The first patch makes printk_ratelimited pass on the return value from printk.
Version 3 gives the temporary return variable a unique name to avoid name
clashes.

The second patch moves the RCU string header and updates the BTRFS code that
depends on it. Version 3 adds the __rcu annotation to the relevant functions.

Version 3 also adds Paul's ack and Josh's review.

Omar Sandoval (2):
  Return a value from printk_ratelimited
  Move BTRFS RCU string to common library

 fs/btrfs/check-integrity.c |  6 +--
 fs/btrfs/dev-replace.c     | 19 +++++-----
 fs/btrfs/disk-io.c         |  6 +--
 fs/btrfs/extent_io.c       |  4 +-
 fs/btrfs/ioctl.c           |  4 +-
 fs/btrfs/raid56.c          |  2 +-
 fs/btrfs/rcu-string.h      | 56 ----------------------------
 fs/btrfs/scrub.c           | 15 ++++----
 fs/btrfs/super.c           |  2 +-
 fs/btrfs/volumes.c         | 14 +++----
 include/linux/printk.h     |  4 +-
 include/linux/rcustring.h  | 92 ++++++++++++++++++++++++++++++++++++++++++++++
 12 files changed, 132 insertions(+), 92 deletions(-)
 delete mode 100644 fs/btrfs/rcu-string.h
 create mode 100644 include/linux/rcustring.h

-- 
2.1.1

[PATCH v3 1/2] Return a value from printk_ratelimited

[Omar Sandoval]

printk returns an integer; there's no reason for printk_ratelimited to swallow
it.

Signed-off-by: Omar Sandoval <osandov@osandov.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/printk.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/linux/printk.h b/include/linux/printk.h
index d78125f..89bb7ab 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -343,12 +343,14 @@ extern asmlinkage void dump_stack(void) __cold;
 #ifdef CONFIG_PRINTK
 #define printk_ratelimited(fmt, ...)					\
 ({									\
+	int __ret_printk_ratelimited = 0;				\
 	static DEFINE_RATELIMIT_STATE(_rs,				\
 				      DEFAULT_RATELIMIT_INTERVAL,	\
 				      DEFAULT_RATELIMIT_BURST);		\
 									\
 	if (__ratelimit(&_rs))						\
-		printk(fmt, ##__VA_ARGS__);				\
+		__ret_printk_ratelimited = printk(fmt, ##__VA_ARGS__);	\
+	__ret_printk_ratelimited;					\
 })
 #else
 #define printk_ratelimited(fmt, ...)					\
-- 
2.1.1

[PATCH v3 2/2] Move BTRFS RCU string to common library

[Omar Sandoval]

The RCU-friendly string API used internally by BTRFS is generic enough for
common use. This doesn't add any new functionality, but instead just moves the
code and documents the existing API.

Signed-off-by: Omar Sandoval <osandov@osandov.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 fs/btrfs/check-integrity.c |  6 +--
 fs/btrfs/dev-replace.c     | 19 +++++-----
 fs/btrfs/disk-io.c         |  6 +--
 fs/btrfs/extent_io.c       |  4 +-
 fs/btrfs/ioctl.c           |  4 +-
 fs/btrfs/raid56.c          |  2 +-
 fs/btrfs/rcu-string.h      | 56 ----------------------------
 fs/btrfs/scrub.c           | 15 ++++----
 fs/btrfs/super.c           |  2 +-
 fs/btrfs/volumes.c         | 14 +++----
 include/linux/rcustring.h  | 92 ++++++++++++++++++++++++++++++++++++++++++++++
 11 files changed, 129 insertions(+), 91 deletions(-)
 delete mode 100644 fs/btrfs/rcu-string.h
 create mode 100644 include/linux/rcustring.h

diff --git a/fs/btrfs/check-integrity.c b/fs/btrfs/check-integrity.c
index ce92ae3..4ccd7da 100644
--- a/fs/btrfs/check-integrity.c
+++ b/fs/btrfs/check-integrity.c
@@ -94,6 +94,7 @@
 #include <linux/mutex.h>
 #include <linux/genhd.h>
 #include <linux/blkdev.h>
+#include <linux/rcustring.h>
 #include "ctree.h"
 #include "disk-io.h"
 #include "hash.h"
@@ -103,7 +104,6 @@
 #include "print-tree.h"
 #include "locking.h"
 #include "check-integrity.h"
-#include "rcu-string.h"
 
 #define BTRFSIC_BLOCK_HASHTABLE_SIZE 0x10000
 #define BTRFSIC_BLOCK_LINK_HASHTABLE_SIZE 0x10000
@@ -851,8 +851,8 @@ static int btrfsic_process_superblock_dev_mirror(
 			printk_in_rcu(KERN_INFO "New initial S-block (bdev %p, %s)"
 				     " @%llu (%s/%llu/%d)\n",
 				     superblock_bdev,
-				     rcu_str_deref(device->name), dev_bytenr,
-				     dev_state->name, dev_bytenr,
+				     rcu_string_dereference(device->name),
+				     dev_bytenr, dev_state->name, dev_bytenr,
 				     superblock_mirror_num);
 		list_add(&superblock_tmp->all_blocks_node,
 			 &state->all_blocks_list);
diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index eea26e1..87d10cc 100644
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -25,6 +25,7 @@
 #include <linux/capability.h>
 #include <linux/kthread.h>
 #include <linux/math64.h>
+#include <linux/rcustring.h>
 #include <asm/div64.h>
 #include "ctree.h"
 #include "extent_map.h"
@@ -34,7 +35,6 @@
 #include "volumes.h"
 #include "async-thread.h"
 #include "check-integrity.h"
-#include "rcu-string.h"
 #include "dev-replace.h"
 #include "sysfs.h"
 
@@ -376,9 +376,9 @@ int btrfs_dev_replace_start(struct btrfs_root *root,
 	printk_in_rcu(KERN_INFO
 		      "BTRFS: dev_replace from %s (devid %llu) to %s started\n",
 		      src_device->missing ? "<missing disk>" :
-		        rcu_str_deref(src_device->name),
+		      rcu_string_dereference(src_device->name),
 		      src_device->devid,
-		      rcu_str_deref(tgt_device->name));
+		      rcu_string_dereference(tgt_device->name));
 
 	tgt_device->total_bytes = src_device->total_bytes;
 	tgt_device->disk_total_bytes = src_device->disk_total_bytes;
@@ -528,9 +528,10 @@ static int btrfs_dev_replace_finishing(struct btrfs_fs_info *fs_info,
 		printk_in_rcu(KERN_ERR
 			      "BTRFS: btrfs_scrub_dev(%s, %llu, %s) failed %d\n",
 			      src_device->missing ? "<missing disk>" :
-			        rcu_str_deref(src_device->name),
+			      rcu_string_dereference(src_device->name),
 			      src_device->devid,
-			      rcu_str_deref(tgt_device->name), scrub_ret);
+			      rcu_string_dereference(tgt_device->name),
+			      scrub_ret);
 		btrfs_dev_replace_unlock(dev_replace);
 		mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);
 		mutex_unlock(&root->fs_info->chunk_mutex);
@@ -544,9 +545,9 @@ static int btrfs_dev_replace_finishing(struct btrfs_fs_info *fs_info,
 	printk_in_rcu(KERN_INFO
 		      "BTRFS: dev_replace from %s (devid %llu) to %s) finished\n",
 		      src_device->missing ? "<missing disk>" :
-		        rcu_str_deref(src_device->name),
+		      rcu_string_dereference(src_device->name),
 		      src_device->devid,
-		      rcu_str_deref(tgt_device->name));
+		      rcu_string_dereference(tgt_device->name));
 	tgt_device->is_tgtdev_for_dev_replace = 0;
 	tgt_device->devid = src_device->devid;
 	src_device->devid = BTRFS_DEV_REPLACE_DEVID;
@@ -805,10 +806,10 @@ static int btrfs_dev_replace_kthread(void *data)
 		printk_in_rcu(KERN_INFO
 			"BTRFS: continuing dev_replace from %s (devid %llu) to %s @%u%%\n",
 			dev_replace->srcdev->missing ? "<missing disk>" :
-			rcu_str_deref(dev_replace->srcdev->name),
+			rcu_string_dereference(dev_replace->srcdev->name),
 			dev_replace->srcdev->devid,
 			dev_replace->tgtdev ?
-			rcu_str_deref(dev_replace->tgtdev->name) :
+			rcu_string_dereference(dev_replace->tgtdev->name) :
 			"<missing target disk>",
 			(unsigned int)progress);
 	}
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index a1d36e6..00f7441 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -31,6 +31,7 @@
 #include <linux/ratelimit.h>
 #include <linux/uuid.h>
 #include <linux/semaphore.h>
+#include <linux/rcustring.h>
 #include <asm/unaligned.h>
 #include "ctree.h"
 #include "disk-io.h"
@@ -44,7 +45,6 @@
 #include "free-space-cache.h"
 #include "inode-map.h"
 #include "check-integrity.h"
-#include "rcu-string.h"
 #include "dev-replace.h"
 #include "raid56.h"
 #include "sysfs.h"
@@ -3059,7 +3059,7 @@ static void btrfs_end_buffer_write_sync(struct buffer_head *bh, int uptodate)
 
 		printk_ratelimited_in_rcu(KERN_WARNING "BTRFS: lost page write due to "
 					  "I/O error on %s\n",
-					  rcu_str_deref(device->name));
+					  rcu_string_dereference(device->name));
 		/* note, we dont' set_buffer_write_io_error because we have
 		 * our own ways of dealing with the IO errors
 		 */
@@ -3247,7 +3247,7 @@ static int write_dev_flush(struct btrfs_device *device, int wait)
 
 		if (bio_flagged(bio, BIO_EOPNOTSUPP)) {
 			printk_in_rcu("BTRFS: disabling barriers on dev %s\n",
-				      rcu_str_deref(device->name));
+				      rcu_string_dereference(device->name));
 			device->nobarriers = 1;
 		} else if (!bio_flagged(bio, BIO_UPTODATE)) {
 			ret = -EIO;
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index af0359d..441dccd 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -11,6 +11,7 @@
 #include <linux/pagevec.h>
 #include <linux/prefetch.h>
 #include <linux/cleancache.h>
+#include <linux/rcustring.h>
 #include "extent_io.h"
 #include "extent_map.h"
 #include "ctree.h"
@@ -18,7 +19,6 @@
 #include "volumes.h"
 #include "check-integrity.h"
 #include "locking.h"
-#include "rcu-string.h"
 #include "backref.h"
 
 static struct kmem_cache *extent_state_cache;
@@ -2065,7 +2065,7 @@ int repair_io_failure(struct btrfs_fs_info *fs_info, u64 start,
 	printk_ratelimited_in_rcu(KERN_INFO
 			"BTRFS: read error corrected: ino %lu off %llu "
 		    "(dev %s sector %llu)\n", page->mapping->host->i_ino,
-		    start, rcu_str_deref(dev->name), sector);
+		    start, rcu_string_dereference(dev->name), sector);
 
 	bio_put(bio);
 	return 0;
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 8a8e298..9d4cd72 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -44,6 +44,7 @@
 #include <linux/uuid.h>
 #include <linux/btrfs.h>
 #include <linux/uaccess.h>
+#include <linux/rcustring.h>
 #include "ctree.h"
 #include "disk-io.h"
 #include "transaction.h"
@@ -53,7 +54,6 @@
 #include "locking.h"
 #include "inode-map.h"
 #include "backref.h"
-#include "rcu-string.h"
 #include "send.h"
 #include "dev-replace.h"
 #include "props.h"
@@ -1583,7 +1583,7 @@ static noinline int btrfs_ioctl_resize(struct file *file,
 	new_size *= root->sectorsize;
 
 	printk_in_rcu(KERN_INFO "BTRFS: new size for %s is %llu\n",
-		      rcu_str_deref(device->name), new_size);
+		      rcu_string_dereference(device->name), new_size);
 
 	if (new_size > old_size) {
 		trans = btrfs_start_transaction(root, 0);
diff --git a/fs/btrfs/raid56.c b/fs/btrfs/raid56.c
index 0a6b6e4..eecf738 100644
--- a/fs/btrfs/raid56.c
+++ b/fs/btrfs/raid56.c
@@ -32,6 +32,7 @@
 #include <linux/list_sort.h>
 #include <linux/raid/xor.h>
 #include <linux/vmalloc.h>
+#include <linux/rcustring.h>
 #include <asm/div64.h>
 #include "ctree.h"
 #include "extent_map.h"
@@ -42,7 +43,6 @@
 #include "raid56.h"
 #include "async-thread.h"
 #include "check-integrity.h"
-#include "rcu-string.h"
 
 /* set when additional merges to this rbio are not allowed */
 #define RBIO_RMW_LOCKED_BIT	1
diff --git a/fs/btrfs/rcu-string.h b/fs/btrfs/rcu-string.h
deleted file mode 100644
index 9e111e4..0000000
--- a/fs/btrfs/rcu-string.h
+++ /dev/null
@@ -1,56 +0,0 @@
-/*
- * Copyright (C) 2012 Red Hat.  All rights reserved.
- *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public
- * License v2 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 021110-1307, USA.
- */
-
-struct rcu_string {
-	struct rcu_head rcu;
-	char str[0];
-};
-
-static inline struct rcu_string *rcu_string_strdup(const char *src, gfp_t mask)
-{
-	size_t len = strlen(src) + 1;
-	struct rcu_string *ret = kzalloc(sizeof(struct rcu_string) +
-					 (len * sizeof(char)), mask);
-	if (!ret)
-		return ret;
-	strncpy(ret->str, src, len);
-	return ret;
-}
-
-static inline void rcu_string_free(struct rcu_string *str)
-{
-	if (str)
-		kfree_rcu(str, rcu);
-}
-
-#define printk_in_rcu(fmt, ...) do {	\
-	rcu_read_lock();		\
-	printk(fmt, __VA_ARGS__);	\
-	rcu_read_unlock();		\
-} while (0)
-
-#define printk_ratelimited_in_rcu(fmt, ...) do {	\
-	rcu_read_lock();				\
-	printk_ratelimited(fmt, __VA_ARGS__);		\
-	rcu_read_unlock();				\
-} while (0)
-
-#define rcu_str_deref(rcu_str) ({				\
-	struct rcu_string *__str = rcu_dereference(rcu_str);	\
-	__str->str;						\
-})
diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index f4a41f3..62e335f 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -18,6 +18,7 @@
 
 #include <linux/blkdev.h>
 #include <linux/ratelimit.h>
+#include <linux/rcustring.h>
 #include "ctree.h"
 #include "volumes.h"
 #include "disk-io.h"
@@ -27,7 +28,6 @@
 #include "extent_io.h"
 #include "dev-replace.h"
 #include "check-integrity.h"
-#include "rcu-string.h"
 #include "raid56.h"
 
 /*
@@ -519,7 +519,8 @@ static int scrub_print_warning_inode(u64 inum, u64 offset, u64 root,
 		printk_in_rcu(KERN_WARNING "BTRFS: %s at logical %llu on dev "
 			"%s, sector %llu, root %llu, inode %llu, offset %llu, "
 			"length %llu, links %u (path: %s)\n", swarn->errstr,
-			swarn->logical, rcu_str_deref(swarn->dev->name),
+			swarn->logical,
+			rcu_string_dereference(swarn->dev->name),
 			(unsigned long long)swarn->sector, root, inum, offset,
 			min(isize - offset, (u64)PAGE_SIZE), nlink,
 			(char *)(unsigned long)ipath->fspath->val[i]);
@@ -531,7 +532,7 @@ err:
 	printk_in_rcu(KERN_WARNING "BTRFS: %s at logical %llu on dev "
 		"%s, sector %llu, root %llu, inode %llu, offset %llu: path "
 		"resolving failed with ret=%d\n", swarn->errstr,
-		swarn->logical, rcu_str_deref(swarn->dev->name),
+		swarn->logical, rcu_string_dereference(swarn->dev->name),
 		(unsigned long long)swarn->sector, root, inum, offset, ret);
 
 	free_ipath(ipath);
@@ -595,7 +596,7 @@ static void scrub_print_warning(const char *errstr, struct scrub_block *sblock)
 				"BTRFS: %s at logical %llu on dev %s, "
 				"sector %llu: metadata %s (level %d) in tree "
 				"%llu\n", errstr, swarn.logical,
-				rcu_str_deref(dev->name),
+				rcu_string_dereference(dev->name),
 				(unsigned long long)swarn.sector,
 				ref_level ? "node" : "leaf",
 				ret < 0 ? -1 : ref_level,
@@ -796,7 +797,7 @@ out:
 			num_uncorrectable_read_errors);
 		printk_ratelimited_in_rcu(KERN_ERR "BTRFS: "
 		    "unable to fixup (nodatasum) error at logical %llu on dev %s\n",
-			fixup->logical, rcu_str_deref(fixup->dev->name));
+		    fixup->logical, rcu_string_dereference(fixup->dev->name));
 	}
 
 	btrfs_free_path(path);
@@ -1198,7 +1199,7 @@ corrected_error:
 			spin_unlock(&sctx->stat_lock);
 			printk_ratelimited_in_rcu(KERN_ERR
 				"BTRFS: fixed up error at logical %llu on dev %s\n",
-				logical, rcu_str_deref(dev->name));
+				logical, rcu_string_dereference(dev->name));
 		}
 	} else {
 did_not_correct_error:
@@ -1207,7 +1208,7 @@ did_not_correct_error:
 		spin_unlock(&sctx->stat_lock);
 		printk_ratelimited_in_rcu(KERN_ERR
 			"BTRFS: unable to fixup (regular) error at logical %llu on dev %s\n",
-			logical, rcu_str_deref(dev->name));
+			logical, rcu_string_dereference(dev->name));
 	}
 
 out:
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index c4124de..cf4db62 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -42,6 +42,7 @@
 #include <linux/cleancache.h>
 #include <linux/ratelimit.h>
 #include <linux/btrfs.h>
+#include <linux/rcustring.h>
 #include "delayed-inode.h"
 #include "ctree.h"
 #include "disk-io.h"
@@ -54,7 +55,6 @@
 #include "volumes.h"
 #include "export.h"
 #include "compression.h"
-#include "rcu-string.h"
 #include "dev-replace.h"
 #include "free-space-cache.h"
 #include "backref.h"
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 2c2d6d1..ada5f86 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -27,6 +27,7 @@
 #include <linux/kthread.h>
 #include <linux/raid/pq.h>
 #include <linux/semaphore.h>
+#include <linux/rcustring.h>
 #include <asm/div64.h>
 #include "ctree.h"
 #include "extent_map.h"
@@ -37,7 +38,6 @@
 #include "raid56.h"
 #include "async-thread.h"
 #include "check-integrity.h"
-#include "rcu-string.h"
 #include "math.h"
 #include "dev-replace.h"
 #include "sysfs.h"
@@ -6322,7 +6322,7 @@ static int update_dev_stat_item(struct btrfs_trans_handle *trans,
 	if (ret < 0) {
 		printk_in_rcu(KERN_WARNING "BTRFS: "
 			"error %d while searching for dev_stats item for device %s!\n",
-			      ret, rcu_str_deref(device->name));
+			      ret, rcu_string_dereference(device->name));
 		goto out;
 	}
 
@@ -6333,7 +6333,7 @@ static int update_dev_stat_item(struct btrfs_trans_handle *trans,
 		if (ret != 0) {
 			printk_in_rcu(KERN_WARNING "BTRFS: "
 				"delete too small dev_stats item for device %s failed %d!\n",
-				      rcu_str_deref(device->name), ret);
+				rcu_string_dereference(device->name), ret);
 			goto out;
 		}
 		ret = 1;
@@ -6346,8 +6346,8 @@ static int update_dev_stat_item(struct btrfs_trans_handle *trans,
 					      &key, sizeof(*ptr));
 		if (ret < 0) {
 			printk_in_rcu(KERN_WARNING "BTRFS: "
-					  "insert dev_stats item for device %s failed %d!\n",
-				      rcu_str_deref(device->name), ret);
+				      "insert dev_stats item for device %s failed %d!\n",
+				      rcu_string_dereference(device->name), ret);
 			goto out;
 		}
 	}
@@ -6401,7 +6401,7 @@ static void btrfs_dev_stat_print_on_error(struct btrfs_device *dev)
 		return;
 	printk_ratelimited_in_rcu(KERN_ERR "BTRFS: "
 			   "bdev %s errs: wr %u, rd %u, flush %u, corrupt %u, gen %u\n",
-			   rcu_str_deref(dev->name),
+			   rcu_string_dereference(dev->name),
 			   btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_WRITE_ERRS),
 			   btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_READ_ERRS),
 			   btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_FLUSH_ERRS),
@@ -6421,7 +6421,7 @@ static void btrfs_dev_stat_print_on_load(struct btrfs_device *dev)
 
 	printk_in_rcu(KERN_INFO "BTRFS: "
 		   "bdev %s errs: wr %u, rd %u, flush %u, corrupt %u, gen %u\n",
-	       rcu_str_deref(dev->name),
+	       rcu_string_dereference(dev->name),
 	       btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_WRITE_ERRS),
 	       btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_READ_ERRS),
 	       btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_FLUSH_ERRS),
diff --git a/include/linux/rcustring.h b/include/linux/rcustring.h
new file mode 100644
index 0000000..2dff2ac
--- /dev/null
+++ b/include/linux/rcustring.h
@@ -0,0 +1,92 @@
+/*
+ * RCU-friendly strings
+ *
+ * Copyright (C) 2012 Red Hat.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * 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, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
+ */
+
+#ifndef _LINUX_RCUSTRING_H
+#define _LINUX_RCUSTRING_H
+
+struct rcu_string {
+	struct rcu_head rcu;
+	char str[0];
+};
+
+/**
+ * rcu_string_strdup() - create an RCU string from a string
+ * @src: The string to copy
+ * @flags: Flags for kmalloc
+ */
+static inline struct rcu_string __rcu *rcu_string_strdup(const char *src,
+							 gfp_t flags)
+{
+	struct rcu_string *ret;
+	size_t len = strlen(src) + 1;
+
+	ret = kmalloc(sizeof(*ret) + (len * sizeof(char)), flags);
+	if (!ret)
+		return ret;
+	memcpy(ret->str, src, len);
+	return ret;
+}
+
+/**
+ * rcu_string_free() - free an RCU string
+ * @str: The string
+ */
+static inline void rcu_string_free(struct rcu_string __rcu *str)
+{
+	if (str)
+		kfree_rcu(str, rcu);
+}
+
+/*
+ * rcu_string_dereference() - dereference an RCU string
+ * @str: The string
+ *
+ * Like rcu_dereference, this must be done in an RCU critical section.
+ */
+static inline char *rcu_string_dereference(struct rcu_string __rcu *rcu_str)
+{
+	return rcu_dereference(rcu_str)->str;
+}
+
+/**
+ * printk_in_rcu() - printk in an RCU read-side critical section
+ */
+#define printk_in_rcu(fmt, ...)			\
+({						\
+	int __ret;				\
+	rcu_read_lock();			\
+	__ret = printk(fmt, __VA_ARGS__);	\
+	rcu_read_unlock();			\
+	__ret;					\
+})
+
+/**
+ * printk_ratelimited_in_rcu() - printk in an RCU read-side critical section
+ */
+#define printk_ratelimited_in_rcu(fmt, ...)		\
+({							\
+	int __ret;					\
+	rcu_read_lock();				\
+	__ret = printk_ratelimited(fmt, __VA_ARGS__);	\
+	rcu_read_unlock();				\
+	__ret;						\
+})
+
+#endif
-- 
2.1.1

Re: [PATCH v3 0/2] Move BTRFS RCU string to common library

[Omar Sandoval]

On Fri, Sep 26, 2014 at 10:36:47PM -0700, Omar Sandoval wrote:
> This patch series makes the generic RCU string library used internally by BTRFS
> accessible by anyone.
> 
> The first patch makes printk_ratelimited pass on the return value from printk.
> Version 3 gives the temporary return variable a unique name to avoid name
> clashes.
> 
> The second patch moves the RCU string header and updates the BTRFS code that
> depends on it. Version 3 adds the __rcu annotation to the relevant functions.
> 
> Version 3 also adds Paul's ack and Josh's review.
> 
> Omar Sandoval (2):
>   Return a value from printk_ratelimited
>   Move BTRFS RCU string to common library
> 
>  fs/btrfs/check-integrity.c |  6 +--
>  fs/btrfs/dev-replace.c     | 19 +++++-----
>  fs/btrfs/disk-io.c         |  6 +--
>  fs/btrfs/extent_io.c       |  4 +-
>  fs/btrfs/ioctl.c           |  4 +-
>  fs/btrfs/raid56.c          |  2 +-
>  fs/btrfs/rcu-string.h      | 56 ----------------------------
>  fs/btrfs/scrub.c           | 15 ++++----
>  fs/btrfs/super.c           |  2 +-
>  fs/btrfs/volumes.c         | 14 +++----
>  include/linux/printk.h     |  4 +-
>  include/linux/rcustring.h  | 92 ++++++++++++++++++++++++++++++++++++++++++++++
>  12 files changed, 132 insertions(+), 92 deletions(-)
>  delete mode 100644 fs/btrfs/rcu-string.h
>  create mode 100644 include/linux/rcustring.h
> 

I forgot to mention: this patch series is against 3.17-rc6.

-- 
Omar

Re: [PATCH v3 1/2] Return a value from printk_ratelimited

[Joe Perches]

On Fri, 2014-09-26 at 22:36 -0700, Omar Sandoval wrote:
> printk returns an integer; there's no reason for printk_ratelimited to swallow
> it.
> 
> Signed-off-by: Omar Sandoval <osandov@osandov.com>
> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> ---

I'd prefer to keep it the way it is actually.

I've submitted several patches to convert the int return
to void for printk derived functions recently.

Re: [PATCH v3 1/2] Return a value from printk_ratelimited

[Omar Sandoval]

On Fri, Sep 26, 2014 at 10:48:11PM -0700, Joe Perches wrote:
> I'd prefer to keep it the way it is actually.
> 
> I've submitted several patches to convert the int return
> to void for printk derived functions recently.

Alright, it doesn't seem like anyone feels strongly for keeping the return
values, so I'll go ahead and submit a v4 that doesn't modify printk_ratelimited
and doesn't return anything from the printk functions in rcustring.h unless
there are any objections.

-- 
Omar