include/trace/events/writeback.h: fix -Wstringop-truncation warnings

There are many of those warnings.

In file included from ./arch/powerpc/include/asm/paca.h:15,
                 from ./arch/powerpc/include/asm/current.h:13,
                 from ./include/linux/thread_info.h:21,
                 from ./include/asm-generic/preempt.h:5,
                 from ./arch/powerpc/include/generated/asm/preempt.h:1,
                 from ./include/linux/preempt.h:78,
                 from ./include/linux/spinlock.h:51,
                 from fs/fs-writeback.c:19:
In function 'strncpy',
    inlined from 'perf_trace_writeback_page_template' at
./include/trace/events/writeback.h:56:1:
./include/linux/string.h:260:9: warning: '__builtin_strncpy' specified
bound 32 equals destination size [-Wstringop-truncation]
  return __builtin_strncpy(p, q, size);
         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fix it by using the new strscpy_pad() which was introduced in "lib/string:
Add strscpy_pad() function" and will always be NUL-terminated instead of
strncpy().  Also, change strlcpy() to use strscpy_pad() in this file for
consistency.

Link: http://lkml.kernel.org/r/1564075099-27750-1-git-send-email-cai@lca.pw
Fixes: 455b2864 ("writeback: Initial tracing support")
Fixes: 028c2dd1 ("writeback: Add tracing to balance_dirty_pages")
Fixes: e84d0a4f ("writeback: trace event writeback_queue_io")
Fixes: b48c104d ("writeback: trace event bdi_dirty_ratelimit")
Fixes: cc1676d9 ("writeback: Move requeueing when I_SYNC set to writeback_sb_inodes()")
Fixes: 9fb0a7da ("writeback: add more tracepoints")
Signed-off-by: Qian Cai <cai@lca.pw>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Tobin C. Harding <tobin@kernel.org>
Cc: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Joe Perches <joe@perches.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Jann Horn <jannh@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Nitin Gote <nitin.r.gote@intel.com>
Cc: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Cc: Stephen Kitt <steve@sk2.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/trace/events/writeback.h

@@ -66,8 +66,9 @@ DECLARE_EVENT_CLASS(writeback_page_template,
 	),
 
 	TP_fast_assign(
-		strncpy(__entry->name,
-			mapping ? dev_name(inode_to_bdi(mapping->host)->dev) : "(unknown)", 32);
+		strscpy_pad(__entry->name,
+			    mapping ? dev_name(inode_to_bdi(mapping->host)->dev) : "(unknown)",
+			    32);
 		__entry->ino = mapping ? mapping->host->i_ino : 0;
 		__entry->index = page->index;
 	),
@@ -110,7 +111,7 @@ DECLARE_EVENT_CLASS(writeback_dirty_inode_template,
 		struct backing_dev_info *bdi = inode_to_bdi(inode);
 
 		/* may be called for files on pseudo FSes w/ unregistered bdi */
-		strncpy(__entry->name,
+		strscpy_pad(__entry->name,
 			    bdi->dev ? dev_name(bdi->dev) : "(unknown)", 32);
 		__entry->ino		= inode->i_ino;
 		__entry->state		= inode->i_state;
@@ -316,7 +317,7 @@ DECLARE_EVENT_CLASS(writeback_write_inode_template,
 	),
 
 	TP_fast_assign(
-		strncpy(__entry->name,
+		strscpy_pad(__entry->name,
 			    dev_name(inode_to_bdi(inode)->dev), 32);
 		__entry->ino		= inode->i_ino;
 		__entry->sync_mode	= wbc->sync_mode;
@@ -360,8 +361,9 @@ DECLARE_EVENT_CLASS(writeback_work_class,
 		__field(unsigned int, cgroup_ino)
 	),
 	TP_fast_assign(
-		strncpy(__entry->name,
-			wb->bdi->dev ? dev_name(wb->bdi->dev) : "(unknown)", 32);
+		strscpy_pad(__entry->name,
+			    wb->bdi->dev ? dev_name(wb->bdi->dev) :
+			    "(unknown)", 32);
 		__entry->nr_pages = work->nr_pages;
 		__entry->sb_dev = work->sb ? work->sb->s_dev : 0;
 		__entry->sync_mode = work->sync_mode;
@@ -414,7 +416,7 @@ DECLARE_EVENT_CLASS(writeback_class,
 		__field(unsigned int, cgroup_ino)
 	),
 	TP_fast_assign(
-		strncpy(__entry->name, dev_name(wb->bdi->dev), 32);
+		strscpy_pad(__entry->name, dev_name(wb->bdi->dev), 32);
 		__entry->cgroup_ino = __trace_wb_assign_cgroup(wb);
 	),
 	TP_printk("bdi %s: cgroup_ino=%u",
@@ -436,7 +438,7 @@ TRACE_EVENT(writeback_bdi_register,
 		__array(char, name, 32)
 	),
 	TP_fast_assign(
-		strncpy(__entry->name, dev_name(bdi->dev), 32);
+		strscpy_pad(__entry->name, dev_name(bdi->dev), 32);
 	),
 	TP_printk("bdi %s",
 		__entry->name
@@ -461,7 +463,7 @@ DECLARE_EVENT_CLASS(wbc_class,
 	),
 
 	TP_fast_assign(
-		strncpy(__entry->name, dev_name(bdi->dev), 32);
+		strscpy_pad(__entry->name, dev_name(bdi->dev), 32);
 		__entry->nr_to_write	= wbc->nr_to_write;
 		__entry->pages_skipped	= wbc->pages_skipped;
 		__entry->sync_mode	= wbc->sync_mode;
@@ -512,7 +514,7 @@ TRACE_EVENT(writeback_queue_io,
 	),
 	TP_fast_assign(
 		unsigned long *older_than_this = work->older_than_this;
-		strncpy(__entry->name, dev_name(wb->bdi->dev), 32);
+		strscpy_pad(__entry->name, dev_name(wb->bdi->dev), 32);
 		__entry->older	= older_than_this ?  *older_than_this : 0;
 		__entry->age	= older_than_this ?
 				  (jiffies - *older_than_this) * 1000 / HZ : -1;
@@ -598,7 +600,7 @@ TRACE_EVENT(bdi_dirty_ratelimit,
 	),
 
 	TP_fast_assign(
-		strlcpy(__entry->bdi, dev_name(wb->bdi->dev), 32);
+		strscpy_pad(__entry->bdi, dev_name(wb->bdi->dev), 32);
 		__entry->write_bw	= KBps(wb->write_bandwidth);
 		__entry->avg_write_bw	= KBps(wb->avg_write_bandwidth);
 		__entry->dirty_rate	= KBps(dirty_rate);
@@ -663,7 +665,7 @@ TRACE_EVENT(balance_dirty_pages,
 
 	TP_fast_assign(
 		unsigned long freerun = (thresh + bg_thresh) / 2;
-		strlcpy(__entry->bdi, dev_name(wb->bdi->dev), 32);
+		strscpy_pad(__entry->bdi, dev_name(wb->bdi->dev), 32);
 
 		__entry->limit		= global_wb_domain.dirty_limit;
 		__entry->setpoint	= (global_wb_domain.dirty_limit +
@@ -723,7 +725,7 @@ TRACE_EVENT(writeback_sb_inodes_requeue,
 	),
 
 	TP_fast_assign(
-		strncpy(__entry->name,
+		strscpy_pad(__entry->name,
 			    dev_name(inode_to_bdi(inode)->dev), 32);
 		__entry->ino		= inode->i_ino;
 		__entry->state		= inode->i_state;
@@ -797,7 +799,7 @@ DECLARE_EVENT_CLASS(writeback_single_inode_template,
 	),
 
 	TP_fast_assign(
-		strncpy(__entry->name,
+		strscpy_pad(__entry->name,
 			    dev_name(inode_to_bdi(inode)->dev), 32);
 		__entry->ino		= inode->i_ino;
 		__entry->state		= inode->i_state;