[LU-14779] lctl get_param does invalid DNS lookups

• Type: Task
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.15.0
• Assignee: Andreas Dilger
• Reporter: John Hammond

Description

lctl get_param does DNS lookups to determine if param components may be nids. But it doesn't always choose a sensible component. For example

lctl get_param [e-mail]_unused_count

will do gethostbyname("namespaces.MGC1.2.3.4").

# gdb lctl
...
(gdb) b gethostbyname
Breakpoint 1 at 0x402d10
(gdb) run get_param [e-mail]_unused_count
Starting program: /root/ex/lustre-release/lustre/utils/.libs/lctl get_param [e-mail]_unused_count
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".

Breakpoint 1, gethostbyname (name=0x646070 "namespaces.MGC1.2.3.4") at ../nss/getXXbyYY.c:93
93	{
(gdb) bt
#0  gethostbyname (name=0x646070 "namespaces.MGC1.2.3.4") at ../nss/getXXbyYY.c:93
#1  0x00007ffff7bc6334 in libcfs_ip_str2addr () from /lib64/liblustreapi.so.1
#2  0x00007ffff7bc691f in libcfs_str2nid () from /lib64/liblustreapi.so.1
#3  0x0000000000414558 in clean_path (popt=popt@entry=0x7fffffffe070, 
    path=path@entry=0x7fffffffe4eb "[e-mail]_unused_count") at lustre_cfg.c:770
#4  0x00000000004164ae in jt_lcfg_getparam (argc=2, argv=0x7fffffffe1f0) at lustre_cfg.c:1210
#5  0x00007ffff7bc7911 in Parser_execarg () from /lib64/liblustreapi.so.1
#6  0x0000000000416f59 in lctl_main (argc=3, argv=0x7fffffffe1e8) at lctl.c:562
#7  0x00007ffff71be505 in __libc_start_main (main=0x403160 <main>, argc=3, argv=0x7fffffffe1e8, init=<optimized out>, fini=<optimized out>, 
    rtld_fini=<optimized out>, stack_end=0x7fffffffe1d8) at ../csu/libc-start.c:266
#8  0x000000000040318e in _start ()

Similarly

get_param [e-mail]_stats

will lookup myfs-ost001d.exports.1.2.3.4 and exports.1.2.3.4.

This behavior is because we are using libcfs_str2nid() to detect NIDs. But this function is written to handle hostnames as well as NIDs.

But this is not great for performance, since, in DNS as in life, looking for something that doesn't exist tends to take a lot longer than looking for something that does.