On Fri, 2019-06-14 at 19:58 -0700, Joe Perches wrote: > On Sat, 2019-06-15 at 10:41 +0800, Yan, Zheng wrote: > > On Fri, Jun 14, 2019 at 9:48 PM Jeff Layton <jlayton@xxxxxxxxxx> wrote: > > > The getxattr interface returns a length after filling out the value > > > buffer, and the convention with xattrs is to not NULL terminate string > > > data. > > > > > > CephFS implements some virtual xattrs by using snprintf to fill the > > > buffer, but that always NULL terminates the string. If userland sends > > > down a buffer that is just the right length to hold the text without > > > termination then we end up truncating the value. > > > > > > Factor the formatting piece of vsnprintf into a separate helper > > > function, and have vsnprintf call that and then do the NULL termination > > > afterward. Then add a snprintf_noterm function that calls the new helper > > > to populate the string but skips the termination. > > Is this function really necessary enough to add > the additional stack use to the generic case? > The only alternative I saw was to allocate an extra buffer in the callers, call snprintf to populate that and then copy the result into the destination buffer sans termination. I really would like to avoid that here. Does breaking this code out into a helper add any significant stack usage? I didn't see it that way, but I am quite concerned about not slowing down the generic vsnprintf routine. > Why not add have this function call vsnprintf > and then terminate the string separately? > I don't quite follow what you're suggesting here. vsnprintf is what does the termination today, and we need a function that doesn't do that. -- Jeff Layton <jlayton@xxxxxxxxxx>
