* Accessing structure fields
@ 2007-09-26 20:34 Mike Mason
2007-09-26 22:55 ` Frank Ch. Eigler
0 siblings, 1 reply; 2+ messages in thread
From: Mike Mason @ 2007-09-26 20:34 UTC (permalink / raw)
To: systemTAP
I'm trying to understand why some recent changes in nfs_proc.stp were necessary. There are numerous changes like the following:
- count = $rdata->args.count
- offset = $rdata->args.offset
+ count = $rdata->args->count
+ offset = $rdata->args->offset
rdata is a pointer to a nfs_read_data structure and args is a nfs_readargs structure within nfs_read_data. args is not a pointer, thus the '.' syntax seems correct. However, $rdata->args->count builds fine, while $rdata->args.count fails with the following error:
semantic error: struct/union 'args' is being accessed instead of a member of the struct/union: identifier '$data' at /usr/local/share/systemtap/tapset/nfs_proc.stp:640:17
semantic error: probe_1113 uses invalid operator: operator '.' at /usr/local/share/systemtap/tapset/nfs_proc.stp:640:28
Is '.' supported when accessing structure fields?
Interestingly, the following also builds fine:
uid = $data->inode->i_uid
In this case, inode *is* a pointer.
Mike
^ permalink raw reply [flat|nested] 2+ messages in thread* Re: Accessing structure fields
2007-09-26 20:34 Accessing structure fields Mike Mason
@ 2007-09-26 22:55 ` Frank Ch. Eigler
0 siblings, 0 replies; 2+ messages in thread
From: Frank Ch. Eigler @ 2007-09-26 22:55 UTC (permalink / raw)
To: Mike Mason; +Cc: systemTAP
Mike Mason <mmlnx@us.ibm.com> writes:
> I'm trying to understand why some recent changes in nfs_proc.stp were necessary. There are numerous changes like the following:
>
> - count = $rdata->args.count
> - offset = $rdata->args.offset
> + count = $rdata->args->count
> + offset = $rdata->args->offset
These are correct.
> Is '.' supported when accessing structure fields?
No. Only the "->" operator is used to traverse inclusion/pointer type
links. It automagically does the right thing, though looks a bit
funny. One reason for this is the "." string concatenation operator.
- FChE
^ permalink raw reply [flat|nested] 2+ messages in thread
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2007-09-26 20:34 Accessing structure fields Mike Mason
2007-09-26 22:55 ` Frank Ch. Eigler
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