Differential D51315
vfs_cache: Fix the SDT definition of vfs:fplookup:lookup:done Authored by 0mp on Mon, Jul 14, 11:14 PM. Tags Referenced Files
Details The definition lists struct nameidata as the type Fixes: 07d2145a1717 vfs: add the infrastructure for lockless lookup I've build the kernel with the change and tested that args[0] in vfs:fplookup:lookup:done no longer needs to be cast to struct nameidata * to access its members such as ni_dirp. Here's a sample script: vfs:fplookup:lookup:done /(int64_t)args[0]->ni_dirp < 0 && arg2 == 3/ {
trace(stringof(args[0]->ni_dirp));
}Side note: I could not figure out the right predicates that look sensible to only show successful lookups with actual path names available in ni_dirp. arg2 == 3 seems to help, but it was not enough. (int64_t)args[0]->ni_dirp < 0 did the trick as printable ni_dirp turn out to always be <0 when cast to int64_t, but I don't understand why. Another side note: wouldn't it be nice to create a vfs.d in /usr/lib/dtrace so that we could use the actual enum for arg2 instead of integers? The enum would be: enum cache_fpl_status { CACHE_FPL_STATUS_DESTROYED, CACHE_FPL_STATUS_ABORTED,
CACHE_FPL_STATUS_PARTIAL, CACHE_FPL_STATUS_HANDLED, CACHE_FPL_STATUS_UNSET };
Diff Detail
Event TimelineComment Actions
Just change the type from int to enum cache_fpl_status in the probe definition, and it'll work. dtrace knows about enum names since they're encoded in CTF info. Comment Actions ah, so the actual fix should be: SDT_PROBE_DEFINE3(vfs, fplookup, lookup, done, "struct nameidata *", "enum cache_fpl_status", "bool"); do I understand correctly? I'm not sure if that would work. DTrace seems to not know about the the constants like CACHE_FPL_STATUS_DESTROYED at all. How would the type change fix that? I'll try that later. Maybe DTrace does some magic that makes it work. Comment Actions Alternatively, I've opened another revision that adds the enum to libdtrace/vfs.d, but I suspect that this is not the right fix based on Mark's last comment. Comment Actions After changing the type: root@freebsd:~ # dtrace -n 'vfs:fplookup:lookup:done /args[1] != CACHE_FPL_STATUS_DESTROYED/{stack(); exit(0);}'
dtrace: description 'vfs:fplookup:lookup:done ' matched 1 probe
CPU ID FUNCTION:NAME
0 69081 lookup:done
kernel`cache_fplookup+0xcb4
kernel`namei+0x194
kernel`vn_open_cred+0x592
kernel`openatfp+0x2b3
kernel`sys_open+0x28
kernel`amd64_syscall+0x169
kernel`0xffffffff81094b8b
root@freebsd:~ # dtrace -lv -n vfs:fplookup:lookup:done
ID PROVIDER MODULE FUNCTION NAME
69081 vfs fplookup lookup done
Probe Description Attributes
Identifier Names: Private
Data Semantics: Private
Dependency Class: Unknown
Argument Attributes
Identifier Names: Private
Data Semantics: Private
Dependency Class: ISA
Argument Types
args[0]: struct nameidata *
args[1]: enum cache_fpl_status
args[2]: bool |