Re: [PATCH] perf, tool, record: Fix the header generation for pipe

Eric Dumazet
2011-08-22T15:51:08Z

Le lundi 22 août 2011 à 16:52 +0200, Jiri Olsa a écrit :

> - fd is always file.. the descriptor, which might be pipe, is in output_fd variable
> but, maybe the die call is not necessary.. this should not fail
>
> - the record_file function is called only on debugfs or procfs files:
> events/header_page
> events/header_event
> events/**/format
> printk_formats
> /proc/kallsyms
>
> so I think I need to read the whole file as in current code.
>

You read the file twice. Is it the right fix ?

Once to compute the length to be able to write the output header, once
to process the content.

Are you sure length cannot change between the two phases ?

/proc/kallsyms can definitely change when a module is loaded.

Usually, when input "file" is not seekable or procfs based (fstat()
returns st_size=0), we must load/cache it in memory (or using a
temporary file) to get a consistent view of it.

This is what is done by following commands :

cat /proc/kallsyms | less
less /proc/kallsyms