Date: Sun, 30 Mar 2008 17:07:59 -0600 From: "Heath Nielson" <heathn@gmail.com> To: freebsd-questions@freebsd.org Subject: Non-Blocking write over NFS fails Message-ID: <92e211670803301607w32fc48ffl7438476e4f273cc3@mail.gmail.com>
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Hi all. It's been some time since posted here but I hope someone can see if
I'm doing something stupid or if I really have found a problem.
On my FreeBSD 7 client (192.168.0.50) I mounted an NFS-share from a FreeBSD 7
server (192.168.0.5). When I try to write a large file from the client to the
share in non-blocking mode, the write() call always returns EAGAIN. I whipped
up a small little test program to illustrate the behavior:
#include <fcntl.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/uio.h>
#include <unistd.h>
int main(int argc, char* argv[]) {
int bufSz = 1172767;
fprintf(stderr, "Creating file: %s\n", argv[1]);
int fd = open(argv[1], O_CREAT|O_RDWR);
if(fd < 0) perror(0);
int ret = fcntl(fd, F_SETFL, O_NONBLOCK);
if(ret < 0) {
perror(0);
}
char* buf = (char*)malloc(bufSz);
memset(buf, 0, bufSz);
ret = -1;
while(ret < 0) {
ret = write(fd, buf, bufSz);
fprintf(stderr, "write: %d\n", ret);
if(ret < 0) perror(0);
sleep(1);
}
free(buf);
close(fd);
return 0;
}
If the size is one byte less (1172766) the write succeeds so I guess I'm
hitting some buffer limit. The mount in an NFSv3 mount and the error occurs
both over UDP and TCP. When I do a tcpdump from the client, I see
(NFS over TCP):
01:47:18.308353 IP 192.168.0.50.835170573 > 192.168.0.5.nfs: 112
lookup fh 1073,399698/4993024 "t.txt"
01:47:18.308548 IP 192.168.0.5.nfs > 192.168.0.50.835170573: reply ok
120 lookup ERROR: No such file or directory
01:47:18.308575 IP 192.168.0.50.835170574 > 192.168.0.5.nfs: 144
create fh 1073,399698/4993024 "t.txt"
01:47:18.308856 IP 192.168.0.5.nfs > 192.168.0.50.835170574: reply ok
272 create fh 1073,399698/4993038
01:47:18.409715 IP 192.168.0.50.859 > 192.168.0.5.nfsd: . ack
2113663444 win 16588 <nop,nop,timestamp 16900146 554159454>
None of the data appears to be sent over the wire. The program loops
indefinitely returning EAGAIN with the write() call. When I run the program
with a smaller buffer size I get:
01:50:31.624967 IP 192.168.0.50.835170584 > 192.168.0.5.nfs: 112
lookup fh 1073,399698/4993024 "t.txt"
01:50:31.625116 IP 192.168.0.5.nfs > 192.168.0.50.835170584: reply ok
120 lookup ERROR: No such file or directory
01:50:31.625140 IP 192.168.0.50.835170585 > 192.168.0.5.nfs: 144
create fh 1073,399698/4993024 "t.txt"
01:50:31.625411 IP 192.168.0.5.nfs > 192.168.0.50.835170585: reply ok
272 create fh 1073,399698/4993039
01:50:31.626582 IP 192.168.0.50.835170586 > 192.168.0.5.nfs: 1448
write fh 1073,399698/4993039 32768 (32768) bytes @ 0
01:50:31.626592 IP 192.168.0.50.0 > 192.168.0.5.nfs: 1448 null
01:50:31.626598 IP 192.168.0.50.0 > 192.168.0.5.nfs: 1448 null
01:50:31.626605 IP 192.168.0.50.0 > 192.168.0.5.nfs: 1448 null
01:50:31.626612 IP 192.168.0.50.0 > 192.168.0.5.nfs: 1448 null
01:50:31.626625 IP 192.168.0.50.0 > 192.168.0.5.nfs: 1448 null
01:50:31.626633 IP 192.168.0.50.0 > 192.168.0.5.nfs: 1448 null
01:50:31.627062 IP 192.168.0.5.nfsd > 192.168.0.50.859: . ack
175520546 win 28946 <nop,nop,timestamp 554352775 17089867>
[....]
01:50:31.726744 IP 192.168.0.5.nfsd > 192.168.0.50.859: . ack 1172801
win 28946 <nop,nop,timestamp 554352874 17089948>
01:50:31.727005 IP 192.168.0.5.nfs > 192.168.0.50.835170621: reply ok
164 write [|nfs]
Since I'm not familiar with the NFS code does anyone know if this should work
(or not)? If it is a problem, where should I go looking for the source of the
problem? I'm assuming somewhere in src/sys/nfsclient.
Thanks,
Heath
(Please CC me since I'm not on the list)
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