sendfile from 9p fs into af_alg

From: Alexei Starovoitov
Date: Tue Nov 22 2016 - 22:58:38 EST

Hi Al,

it seems the following commit 523ac9afc73a ("switch default_file_splice_read() to use of pipe-backed iov_iter")
breaks sendfile from 9p fs into af_alg socket.
sendfile into af_alg is used by iproute2/tc.
I'm not sure whether it's 9p or crypto or vfs problem, but happy to test any patches.

The following program is a reduced test from iproute2.
On broken kernels it fails as:
$ ./a.out some_file
Error from sendfile (8192 vs 9624 bytes): Success

It seems to work fine when 'some_file' is on ext4 or tmpfs, so could be 9p related.

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <stdbool.h>
#include <stdint.h>
#include <errno.h>
#include <fcntl.h>
#include <stdarg.h>
#include <limits.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/un.h>
#include <sys/vfs.h>
#include <sys/mount.h>
#include <sys/syscall.h>
#include <sys/sendfile.h>
#include <sys/resource.h>

#include <linux/if_alg.h>

#include <arpa/inet.h>

#ifndef AF_ALG
#define AF_ALG 38

static int obj_hash(const char *object, uint8_t *out, size_t len)
struct sockaddr_alg alg = {
.salg_family = AF_ALG,
.salg_type = "hash",
.salg_name = "sha1",
int ret, cfd, ofd, ffd;
struct stat stbuff;
ssize_t size;

if (!object || len != 20)
return -EINVAL;

cfd = socket(AF_ALG, SOCK_SEQPACKET, 0);
if (cfd < 0) {
fprintf(stderr, "Cannot get AF_ALG socket: %s\n",
return cfd;

ret = bind(cfd, (struct sockaddr *)&alg, sizeof(alg));
if (ret < 0) {
fprintf(stderr, "Error binding socket: %s\n", strerror(errno));
goto out_cfd;

ofd = accept(cfd, NULL, 0);
if (ofd < 0) {
fprintf(stderr, "Error accepting socket: %s\n",
ret = ofd;
goto out_cfd;

ffd = open(object, O_RDONLY);
if (ffd < 0) {
fprintf(stderr, "Error opening object %s: %s\n",
object, strerror(errno));
ret = ffd;
goto out_ofd;

ret = fstat(ffd, &stbuff);
if (ret < 0) {
fprintf(stderr, "Error doing fstat: %s\n",
goto out_ffd;

size = sendfile(ofd, ffd, NULL, stbuff.st_size);
if (size != stbuff.st_size) {
fprintf(stderr, "Error from sendfile (%zd vs %zu bytes): %s\n",
size, stbuff.st_size, strerror(errno));
ret = -1;
goto out_ffd;

size = read(ofd, out, len);
if (size != len) {
fprintf(stderr, "Error from read (%zd vs %zu bytes): %s\n",
size, len, strerror(errno));
ret = -1;
} else {
ret = 0;
return ret;

int main(int ac, char **av)
uint8_t hash[20] = {};

if (ac != 2) {
fprintf(stderr, "%s file\n", av[0]);
return 1;
obj_hash(av[1], hash, sizeof(hash));
printf("hash %llx\n", *(long long *)hash);
return 0;