Thank you for your reply, however I had realized I could do something like that, but it a stanza per iteration of the loop and if the loop can be large (in the case I was looking at well over 4000 entries) the number of stanzas is prohibitive.
I'm looking for a way to actually follow the chain all the way to the end without a hard limit and without a huge dtrace script. Regards, Lida Horn requires On 8/19/2011 2:46 PM, Jonathan Adams wrote:
On Fri, Aug 19, 2011 at 01:34:36PM -0700, Lida Horn wrote:I'm looking for an example of how one could write a dtrace probe that could follow something like a NULL terminated linked list. For example: struct list { struct list *next; void *data; }; struct list *list_root; Assuming I had "list_root" available, but I wanted to know how long the linked list is, how can I do this in a dtrace probe? If I had looping constructs, it would be obvious: int count_list(struct list *list) { int i; for (i = 0; list != NULL; list = list->next) ++i; return i; } In the dtrace scripting language there are no loop constructs, but is there a way to add a new provider than can loop?Generally, you can do this using something like: my:probe:matching:func { this->list = /* some way to get initial list */; this->length = 0; } my:probe:matching:func / this->list != NULL / { this->list = this->list->next; this->length++; } my:probe:matching:func / this->list != NULL / { this->list = this->list->next; this->length++; } my:probe:matching:func / this->list != NULL / { this->list = this->list->next; this->length++; } my:probe:matching:func / this->list != NULL / { this->list = this->list->next; this->length++; } /* repeat N times, where N is the max list length */ my:probe:matching:func / this->list != NULL / { /* list was longer than our maximum length */ @overflow = count(); } my:probe:matching:func / this->list == NULL / { /* use this->count as the length of the list */ } (Enablings for a probe are guaranteed to execute in program order, and this-> variables are valid between enablings of the same probe.) Cheers, - jonathan
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