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authorChristophe Leroy <christophe.leroy@c-s.fr>2015-05-06 17:26:47 +0200
committerWilly Tarreau <w@1wt.eu>2015-12-06 00:49:20 +0100
commit1524cdaae2c0c971a62423b8132620d62d0aa0f5 (patch)
treefbec8ba53198450d78dd11827786747e1767a253
parente3478e8ce2b45f38be09d82689af2afed509fcb8 (diff)
splice: sendfile() at once fails for big files
commit 0ff28d9f4674d781e492bcff6f32f0fe48cf0fed upstream. 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. /* 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@c-s.fr> Signed-off-by: Jens Axboe <axboe@fb.com> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> (cherry picked from commit fcb2781782b61631db4ed31e98757795eacd31cb) Signed-off-by: Willy Tarreau <w@1wt.eu>
-rw-r--r--fs/splice.c12
1 files changed, 11 insertions, 1 deletions
diff --git a/fs/splice.c b/fs/splice.c
index 1ef1c008dc7a..5c006c8bba5d 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -1123,7 +1123,7 @@ 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
@@ -1166,6 +1166,7 @@ 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;
@@ -1179,6 +1180,15 @@ ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd,
sd->total_len = read_len;
/*
+ * If more data is pending, set SPLICE_F_MORE
+ * If this is the last data and SPLICE_F_MORE was not set
+ * initially, clears it.
+ */
+ 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
* could get stuck data in the internal pipe: