Messages in this thread | | | Date | Fri, 16 Jul 2021 14:37:05 -0400 | From | Steven Rostedt <> | Subject | Re: [GIT PULL] tracing: histogram fix and take 2 on the __string_len() marcros |
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On Fri, 16 Jul 2021 11:11:38 -0700 Linus Torvalds <torvalds@linux-foundation.org> wrote:
> On Thu, Jul 15, 2021 at 6:57 PM Steven Rostedt <rostedt@goodmis.org> wrote: > > > > tracing: One fix in the histogram code and another take at the __string_len() macro > > What part of "strncpy()" is garbage did I not make clear?
So how do you want this implemented?
#define __assign_str_len(dst, src, len) \ do { \ strscpy(__get_str(dst), (src) ? (const char *)(src) : "(null)", len); \ __get_str(dst)[len] = '\0'; \ } while(0)
I could even do:
#define __assign_str_len(dst, src, len) \ do { \ if (!src && len > 6) \ len = 6; \ memcpy(__get_str(dst), (src) ? (const char *)(src) : "(null)", len); \ __get_str(dst)[len] = '\0'; \ } while(0)
Which would work just as well, although I had to account if len is greater than "(null)". Which should never happen, but I have it there, because I copied the code from the __string() version which uses strlen() and that would break if a null is passed in (which in rare cases happen). But it would actually be a bug to use __string_len() in a place that can take a NULL, unless len was zero.
Not sure how the above is any different than using strncpy().
Again, src is a string without a '\0'. What I don't understand is how strscpy() is any better than strncpy() in this situation?
As I replied to you last time, the dst is created by allocating 'len + 1' on the ring buffer, and len is to be no greater than the number of characters in src.
The only purpose to use this is to either truncate a string, or to pass in a string that was read from a memory location that does not have a terminating '\0' in it, but you know the length of the string. If you have a normal string, simply use the __string() which uses strlen() to calculate the required space.
It's basically this:
dst = malloc(len + 1); memcpy(dst, src, len); dst[len] = '\0';
"strncpy() is garbage" does not compute to me in the above usage.
-- Steve
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