Re: [PATCH v2 1/2] tracing/events: make __string() more general

From: Christoph Hellwig
Date: Wed May 27 2009 - 03:36:58 EST

On Wed, May 27, 2009 at 09:43:32AM +0800, Li Zefan wrote:
> I'm not suffering from NULL str, so I'm not quite sure how you want __string()
> deal with it.

The internals of __string is still magic to me, need to finish my
advance cpp abuse degree first ;-)

But the expected outcome would be that when we get a NULL pointer as
input we get a NULL pointer as output again.

What I currently do is:

TP_PROTO(struct xfs_da_args *args, int i, int j, int count),
TP_ARGS(args, i, j, count),

__field(xfs_ino_t, ino)
__array(char, name, TRACE_MAXNAMELEN)
__field(int, namelen)

__entry->ino = args->dp->i_ino;
if (args->namelen)
memcpy(__entry->name, args->name,
min(args->namelen, TRACE_MAXNAMELEN));
__entry->namelen = args->namelen;

TP_printk("ino 0x%lld %pF name %.*s namelen %d hashval 0x%x "
"inumber 0x%llx op_flags %s i %d j %d count %d",
(void *)__entry->caller_ip,
min(__entry->namelen, TRACE_MAXNAMELEN),
__entry->namelen ? __entry->name : NULL,

---end quoted text---
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