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SubjectRe: sed not working on /proc files
On Mon, Apr 26, 1999 at 09:15:56PM -0400, Richard B. Johnson wrote:
> On Mon, 26 Apr 1999, Chip Salzenberg wrote:
> > According to Jeremy Fitzhardinge:
> > > On 26-Apr-99 Stefan Monnier wrote:
> > > > open("/proc/meminfo", O_RDONLY) = 3
> > > > fstat(3, {st_mode=0, st_size=0, ...}) = 0
> > > > mmap(0, 0, PROT_READ, MAP_PRIVATE, 3, 0) = 0
> > > This is the problem. It stats the file, mmaps 0 bytes from it and finishes
> > > with no action. Presumeably if the mmap failed or stat said the file isn't a
> > > regular file it would use normal read.
> > Hm. Would it be a Bad Thing for mmap to fail on /proc files that
> > don't report true sizes?
> I don't know. And I don't know how to make it fail. I understand that
> the reason why most sizes are not reported are that sizes are dynamic,
> i.e., /proc/interrupts is bigger each time a value increase over 10. Since
> the /proc file-system does know when a directory access is made, it
> might be a good idea to actually calculate the length (but only at
> directory access time, not when data are being accumumated which would
> be a large overhead that is wasted because /proc is seldom read.

> It is also possible to just return a size of, maybe, 1024 bytes for
> each of the files that are normally 0 size. I don't think a premature
> EOF would affect most Unix tools. This would have zero overhead and
> might make life easier.

/proc files could pretend to be pipes. Would it spoil any programme behaviour?

R.

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