If the kernel receives a negative nsid it will automatically assign the next available nsid. In this case alloc_netid() will set min and max to 0 for ird_alloc(). And when max == 0 idr_alloc() will interpret this as the maxium range, i.e. specific to nsids it will try to find an id in the range [0,INT_MAX). This is intentionally supported in the kernel for nsids. Commit acbe9118ce8086f765ffb0da15f80c7c01a8903a regressed ip netns in that respect although previously the use-case was either accidentally supported or opaquely supported such that it triggered the original commit. From what I can gather it went as follows before: atoi() was called with a string indicating a negative value which caused it to return -1 which was passed to the kernel. Let's make it less opaque by introducing the keyword "auto":
ip netns set <netns-name> auto will cause nsid to be set to -1 and the kernel will select an available nsid. Signed-off-by: Christian Brauner <christian.brau...@ubuntu.com> --- ChangeLog v0->v1: * introduce "auto" keyword for ip netns to automatically allocate an available nsid --- ip/ipnetns.c | 5 ++++- man/man8/ip-netns.8 | 1 + 2 files changed, 5 insertions(+), 1 deletion(-) diff --git a/ip/ipnetns.c b/ip/ipnetns.c index 059a4220..631794b8 100644 --- a/ip/ipnetns.c +++ b/ip/ipnetns.c @@ -718,7 +718,10 @@ static int netns_set(int argc, char **argv) return -1; } name = argv[0]; - if (get_unsigned(&nsid, argv[1], 0)) + /* If a negative nsid is specified the kernel will select the nsid. */ + if (strcmp(argv[1], "auto") == 0) + nsid = -1; + else if (get_unsigned(&nsid, argv[1], 0)) invarg("Invalid \"netnsid\" value\n", argv[1]); snprintf(netns_path, sizeof(netns_path), "%s/%s", NETNS_RUN_DIR, name); diff --git a/man/man8/ip-netns.8 b/man/man8/ip-netns.8 index c5310e24..d539f18b 100644 --- a/man/man8/ip-netns.8 +++ b/man/man8/ip-netns.8 @@ -137,6 +137,7 @@ $ ip netns del net0 .sp This command assigns a id to a peer network namespace. This id is valid only in the current network namespace. +If the keyword "auto" is specified an available nsid will be chosen. This id will be used by the kernel in some netlink messages. If no id is assigned when the kernel needs it, it will be automatically assigned by the kernel. -- 2.14.1