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netlink: Change rtnl_dump_done to always show error 

The original code which became rtnl_dump_done only shows netlink errors
if the protocol is NETLINK_SOCK_DIAG, but netlink dumps always appends
the length which contains any error encountered during the dump. Update
rtnl_dump_done to always show the error if there is one.

As an *example* without this patch, dumping a route object that exceeds
the internal buffer size terminates with no message to the user -- the
dump just ends because the NLMSG_DONE attribute was received. With this
patch the user at least gets a message that the dump was aborted.

$ ip ro ls
default via 10.0.2.2 dev eth0
10.0.2.0/24 dev eth0 proto kernel scope link src 10.0.2.15
10.10.0.0/16 dev veth1 proto kernel scope link src 10.10.0.1
172.16.1.0/24 dev br0.11 proto kernel scope link src 172.16.1.1
Error: Buffer too small for object
Dump terminated

The point of this patch is to notify the user of a failure versus
silently exiting on a partial dump. Because the NLMSG_DONE attribute
was received, the entire dump needs to be restarted to use a larger
buffer for EMSGSIZE errors. That could be done automatically but it
has other user impacts (e.g., duplicate output if the dump is
restarted) and should be the subject of a different patch.

Signed-off-by: David Ahern <dsahern@gmail.com>
This commit is contained in:
David Ahern 2017-05-16 14:22:46 -07:00 committed by Stephen Hemminger
parent 98447086f8
commit 05a14fc121
1 changed files with 20 additions and 14 deletions
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34
lib/libnetlink.c
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@ -266,21 +266,27 @@ static int rtnl_dump_done(const struct rtnl_handle *rth,
{
int len = *(int *)NLMSG_DATA(h);
if (rth->proto == NETLINK_SOCK_DIAG) {
if (h->nlmsg_len < NLMSG_LENGTH(sizeof(int))) {
fprintf(stderr, "DONE truncated\n");
return -1;
}
if (len < 0) {
errno = -len;
if (errno == ENOENT || errno == EOPNOTSUPP)
return -1;
perror("RTNETLINK answers");
return len;
}
if (h->nlmsg_len < NLMSG_LENGTH(sizeof(int))) {
fprintf(stderr, "DONE truncated\n");
return -1;
}
if (len < 0) {
errno = -len;
switch (errno) {
case ENOENT:
case EOPNOTSUPP:
return -1;
case EMSGSIZE:
fprintf(stderr,
"Error: Buffer too small for object.\n");
break;
default:
perror("RTNETLINK answers");
}
return len;
}
return 0;
}