Christophe Leroy <christophe.leroy@xxxxxx> wrote:
> Using sendfile with below small program to get MD5 sums of some files,
> it appear that big files (over 64kbytes with 4k pages system) get a
> wrong MD5 sum while small files get the correct sum.
> This program uses sendfile() to send a file to an AF_ALG socket
> for hashing.
Jens, any comments on this patch?
> /* md5sum2.c */
> #include <stdio.h>
> #include <stdlib.h>
> #include <unistd.h>
> #include <string.h>
> #include <fcntl.h>
> #include <sys/socket.h>
> #include <sys/stat.h>
> #include <sys/types.h>
> #include <linux/if_alg.h>
>
> int main(int argc, char **argv)
> {
> int sk = socket(AF_ALG, SOCK_SEQPACKET, 0);
> struct stat st;
> struct sockaddr_alg sa = {
> .salg_family = AF_ALG,
> .salg_type = "hash",
> .salg_name = "md5",
> };
> int n;
>
> bind(sk, (struct sockaddr*)&sa, sizeof(sa));
>
> for (n = 1; n < argc; n++) {
> int size;
> int offset = 0;
> char buf[4096];
> int fd;
> int sko;
> int i;
>
> fd = open(argv[n], O_RDONLY);
> sko = accept(sk, NULL, 0);
> fstat(fd, &st);
> size = st.st_size;
> sendfile(sko, fd, &offset, size);
> size = read(sko, buf, sizeof(buf));
> for (i = 0; i < size; i++)
> printf("%2.2x", buf[i]);
> printf(" %s\n", argv[n]);
> close(fd);
> close(sko);
> }
> exit(0);
> }
>
> Test below is done using official linux patch files. First result is
> with a software based md5sum. Second result is with the program above.
>
> root@vgoip:~# ls -l patch-3.6.*
> -rw-r--r-- 1 root root 64011 Aug 24 12:01 patch-3.6.2.gz
> -rw-r--r-- 1 root root 94131 Aug 24 12:01 patch-3.6.3.gz
>
> root@vgoip:~# md5sum patch-3.6.*
> b3ffb9848196846f31b2ff133d2d6443 patch-3.6.2.gz
> c5e8f687878457db77cb7158c38a7e43 patch-3.6.3.gz
>
> root@vgoip:~# ./md5sum2 patch-3.6.*
> b3ffb9848196846f31b2ff133d2d6443 patch-3.6.2.gz
> 5fd77b24e68bb24dcc72d6e57c64790e patch-3.6.3.gz
>
>
> After investivation, it appears that sendfile() sends the files by blocks
> of 64kbytes (16 times PAGE_SIZE). The problem is that at the end of each
> block, the SPLICE_F_MORE flag is missing, therefore the hashing operation
> is reset as if it was the end of the file.
>
> This patch adds SPLICE_F_MORE to the flags when more data is pending.
>
> With the patch applied, we get the correct sums:
>
> root@vgoip:~# md5sum patch-3.6.*
> b3ffb9848196846f31b2ff133d2d6443 patch-3.6.2.gz
> c5e8f687878457db77cb7158c38a7e43 patch-3.6.3.gz
>
> root@vgoip:~# ./md5sum2 patch-3.6.*
> b3ffb9848196846f31b2ff133d2d6443 patch-3.6.2.gz
> c5e8f687878457db77cb7158c38a7e43 patch-3.6.3.gz
>
> Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
> ---
> v2: no change, only new commit text
>
> fs/splice.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/fs/splice.c b/fs/splice.c
> index 476024b..fe61723 100644
> --- a/fs/splice.c
> +++ b/fs/splice.c
> @@ -1161,7 +1161,7 @@ ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd,
> long ret, bytes;
> umode_t i_mode;
> size_t len;
> - int i, flags;
> + int i, flags, more;
>
> /*
> * We require the input being a regular file, as we don't want to
> @@ -1204,6 +1204,7 @@ ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd,
> * Don't block on output, we have to drain the direct pipe.
> */
> sd->flags &= ~SPLICE_F_NONBLOCK;
> + more = sd->flags & SPLICE_F_MORE;
>
> while (len) {
> size_t read_len;
> @@ -1216,6 +1217,10 @@ ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd,
> read_len = ret;
> sd->total_len = read_len;
>
> + if (read_len < len)
> + sd->flags |= SPLICE_F_MORE;
> + else if (!more)
> + sd->flags &= ~SPLICE_F_MORE;
> /*
> * NOTE: nonblocking mode only applies to the input. We
> * must not do the output in nonblocking mode as then we
Thanks,
--
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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