Thursday, June 13, 2019

DTrace: nfsv4 provider and utf8string

The nfsv4 provider provides some structures with component4 type which is defined as:

typedef struct {
 uint_t utf8string_len;
 char *utf8string_val;
} utf8string;

typedef utf8string component4;

So for example, to print NFSv4 file renames you have to do:

    this->a = (char *)alloca(args[2]->oldname.utf8string_len + 1);
    bcopy(args[2]->oldname.utf8string_val, this->a, args[2]->oldname.utf8string_len);
    this->a[args[2]->oldname.utf8string_len + 1] = '\0';

    this->b = (char *)alloca(args[2]->newname.utf8string_len + 1);
    bcopy(args[2]->newname.utf8string_val, this->b, args[2]->newname.utf8string_len);
    this->b[args[2]->newname.utf8string_len + 1] = '\0';

    printf("NFSv4 rename: %s\n", strjoin(this->a, strjoin(" -> ", this->b)));

Ideally DTrace (strjoin(), etc.) should deal with utf8string type automatically.

Linux Load Averages

Linux measures load average differently than other OS'es. In a nutshell it includes both CPU and disk i/o and more. Brendan has an excellent blog entry on this explaining in much more detail how it works.