Am Mittwoch, 24. Dezember 2014, 15:10:14 schrieb leroy christophe: Hi leroy, > Le 24/12/2014 10:03, Stephan Mueller a écrit : > > Am Dienstag, 23. Dezember 2014, 18:16:01 schrieb leroy christophe: > > > > Hi leroy, > > > >> Le 20/12/2014 07:37, Stephan Mueller a écrit : > >>> Am Donnerstag, 18. Dezember 2014, 13:22:20 schrieb leroy christophe: > >>> > >>> Hi Christophe, > >>> > >>>> Le 18/12/2014 13:15, Stephan Mueller a écrit : > >>>>> Hi Herbert, > >>>>> > >>>>> While testing the vmsplice/splice interface of algif_hash I was made > >>>>> aware of the problem that data blobs larger than 16 pages do not seem > >>>>> to > >>>>> be hashed properly. > >>>>> > >>>>> For testing, a file is mmap()ed and handed to vmsplice / splice. If > >>>>> the > >>>>> file is smaller than 2**16, the interface returns the proper hash. > >>>>> However, when the file is larger, only the first 2**16 bytes seem to > >>>>> be > >>>>> used. > >>>>> > >>>>> When adding printk's to hash_sendpage, I see that this function is > >>>>> invoked exactly 16 times where the first 15 invocations have the > >>>>> MSG_MORE flag set and the last invocation does not have MSG_MORE. > >>>> > >>>> Hi Stephan, > >>>> > >>>> I have already noticed the same issue and proposed a patch, but I never > >>>> got any feedback and it has never been merged, allthought I pinged it a > >>>> few times. > >>>> > >>>> See https://lkml.org/lkml/2014/4/18/276 > >>> > >>> After testing, this patch does not work for me. The operation still > >>> stops > >>> after 16 pages. > >> > >> Yes, it looks like the function I fixed is exclusively used by > >> sendfile() system call. > >> So there is probably the same kind of fix to be done in another function. > > > > I do not believe that is the case. IMHO the blocking issue is found in the > > following code: > > > > splice_from_pipe_feed walks the pipe->nrbufs. And vmsplice_to_pipe defines > > the maximum number of nrbufs as PIPE_DEF_BUFFERS -- which is 16. As > > subsequent functions allocate memory based on PIPE_DEF_BUFFERS, there is > > no trivial way to increase the number of pages to be processed. > > > > Thus I see that the vmsplice/splice combo can at most operate on a chunk > > of 16 pages. Thus, you have to segment your input buffer into chunks of > > that size and invoke the vmsplice/splice syscalls for each segment. > > Yes your are probably right. There splice needs to be called with > SPLICE_F_MORE flag, hope that works. That is not the only one. Vmsplice works on a pipe. A pipe is backed by 16 pages max. Thus, you have to call vmsplice once per 16 pages. The current code I am testing which seems to work is the following: while (inlen) { size_t datalen = (inlen > MAXLEN) ? MAXLEN : inlen; iov.iov_len = datalen; ret = _kcapi_common_vmsplice_data(handle, &iov, 1, datalen, 1); if (0 > ret) return ret; processed += ret; iov.iov_base = (void*)(uintptr_t)(in + processed); inlen -= ret; } return _kcapi_common_read_data(handle, out, outlen); -- Ciao Stephan -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
