[9fans] how to truncate a file?

[9fans] how to truncate a file?

[YAMANASHI Takeshi]

Is there an idiom for truncationg a file in Plan 9?
I'm suspecting it's not easy because APE ftruncate is written as:

	/sys/src/ape/lib/ap/plan9/ftruncate.c

	int
	ftruncate(int fd, off_t length)
	{
		errno = EINVAL;
		return -1;
	}

There is OTRUNC mode, but I would like to chop off a file from
a certain position to the end of the file.
-- 

Re: [9fans] how to truncate a file?

[geoff]

In theory, wstat with the desired file length will do it, though ken's
fs doesn't implement it currently.  I'll take another look at how hard
it would be to do.

Re: [9fans] how to truncate a file?

[Russ Cox]

ape's ftruncate predates 9P2000.  on fossil you can use

int
ftruncate(int fd, vlong length)
{
    Dir d;
    nulldir(&d);
    d.length = length;
    return dirfwstat(fd, &d);
}

russ

Re: [9fans] how to truncate a file?

[YAMANASHI Takeshi]

On Fri Oct 15 09:42:16 JST 2004, geoff@collyer.net wrote:
> In theory, wstat with the desired file length will do it, though ken's
> fs doesn't implement it currently.

Your theory seems to be approved by Russ's ftruncate.
And also, I was warned that it depends on underlying file server
if it works or not (fossil does while ken's fs doesn't).

Thanks, Geoff and Russ.
-- 

Re: [9fans] how to truncate a file?

[YAMANASHI Takeshi]

On Fri Oct 15 09:53:05 JST 2004, Russ Cox wrote:
> int
> ftruncate(int fd, vlong length)
> {
>     Dir d;
>     nulldir(&d);
>     d.length = length;
>     return dirfwstat(fd, &d);
> }

FYI, I tried and got the following results:

It worked on:
	fossil
	ramfs

It didn't on:
	ken's fs
	kfs

Thanks, again.  I'm fortunate that I had moved to fossil. :)
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