From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <a78c80811d831cabebc5cb1bdbce77c9@quanstro.net>
To: 9fans@9fans.net
From: erik quanstrom <quanstro@quanstro.net>
Date: Fri, 12 Sep 2008 07:47:16 -0400
In-Reply-To: <10b109140809120134v68ff8c5bo43202c0299b247dc@mail.gmail.com>
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Subject: Re: [9fans] patch/create problem (error?)
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>>> I had problem to create a patch - the command didn't finish for long long time.
>>
>> I created a patch yesterday and it worked fine. It is fairly slow as it
>> diff's all the files you have changed with those on sources.
>>
>> Sadly the 9p protocol is quite badly effected by high (intercontinential) RTTs.
>>
>> -Steve
>
> There were only 2 files in the patch. I wait for about 10 minutes and nothing.
> But then I tried to copy a file from command line.
> If I copied an ordinary file (to /n/sources) it was done immediately.
> But If I copied a file from bind-ed(!) directory it was endless...
> There was no diff, only copy file.

i would guess the problem is a bit different.  i'm assuming that
reads from sources work fine.  it's not until you try to write there
that there's a problem.

this sounds like a mtu problem.  i have a similar problem.
i am not able to submit patches over one particular
network interface.  however, if i use a lower mtu, things work fine.
i believe this is because the dumpy dsl modem we have
blocks icmp messages.

you could lower the mtu on the interface, but rather than
punishing all traffic, i wrote a program called cpmtu. cpmtu
is attached.  if you define this function
	fn cp {cpmtu -m 700 $*}
before you run patch/create, i believe patch should work
properly for you.

as an aside: i don't think 9p itself limits plan 9 performance
over high-latency links.  the limitations have more to do with
the number of outstanding messages, which is 1 in the mnt
driver.

- erik

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#include <u.h>
#include <libc.h>

int	mtu	= 8*1024;
int	failed;
int	gflag;
int	uflag;
int	xflag;
void	copy(char *from, char *to, int todir);
int	copy1(int fdf, int fdt, char *from, char *to);

void
usage(void)
{
	fprint(2, "usage:\tcp [-gux] [-m mtu] fromfile tofile\n");
	fprint(2, "\tcp [-x] [-m mtu] fromfile ... todir\n");
	exits("usage");
}

void
main(int argc, char *argv[])
{
	Dir *dirb;
	int todir, i;

	ARGBEGIN {
	case 'g':
		gflag++;
		break;
	case 'u':
		uflag++;
		gflag++;
		break;
	case 'x':
		xflag++;
		break;
	case 'm':
		mtu = atoi(EARGF(usage()));
		if(mtu > 0)
			break;
	default:
		usage();
	} ARGEND

	todir=0;
	if(argc < 2)
		usage();
	dirb = dirstat(argv[argc-1]);
	if(dirb!=nil && (dirb->mode&DMDIR))
		todir=1;
	if(argc>2 && !todir){
		fprint(2, "cp: %s not a directory\n", argv[argc-1]);
		exits("bad usage");
	}
	for(i=0; i<argc-1; i++)
		copy(argv[i], argv[argc-1], todir);
	if(failed)
		exits("errors");
	exits(0);
}

int
samefile(Dir *a, char *an, char *bn)
{
	Dir *b;
	int ret;

	ret = 0;
	b=dirstat(bn);
	if(b != nil)
	if(b->qid.type==a->qid.type)
	if(b->qid.path==a->qid.path)
	if(b->qid.vers==a->qid.vers)
	if(b->dev==a->dev)
	if(b->type==a->type){
		fprint(2, "cp: %s and %s are the same file\n", an, bn);
		ret = 1;
	}
	free(b);
	return ret;
}

void
copy(char *from, char *to, int todir)
{
	Dir *dirb, dirt;
	char name[256];
	int fdf, fdt, mode;

	if(todir){
		char *s, *elem;
		elem=s=from;
		while(*s++)
			if(s[-1]=='/')
				elem=s;
		sprint(name, "%s/%s", to, elem);
		to=name;
	}

	if((dirb=dirstat(from))==nil){
		fprint(2,"cp: can't stat %s: %r\n", from);
		failed = 1;
		return;
	}
	mode = dirb->mode;
	if(mode&DMDIR){
		fprint(2, "cp: %s is a directory\n", from);
		free(dirb);
		failed = 1;
		return;
	}
	if(samefile(dirb, from, to)){
		free(dirb);
		failed = 1;
		return;
	}
	mode &= 0777;
	fdf=open(from, OREAD);
	if(fdf<0){
		fprint(2, "cp: can't open %s: %r\n", from);
		free(dirb);
		failed = 1;
		return;
	}
	fdt=create(to, OWRITE, mode);
	if(fdt<0){
		fprint(2, "cp: can't create %s: %r\n", to);
		close(fdf);
		free(dirb);
		failed = 1;
		return;
	}
	if(copy1(fdf, fdt, from, to)==0 && (xflag || gflag || uflag)){
		nulldir(&dirt);
		if(xflag){
			dirt.mtime = dirb->mtime;
			dirt.mode = dirb->mode;
		}
		if(uflag)
			dirt.uid = dirb->uid;
		if(gflag)
			dirt.gid = dirb->gid;
		if(dirfwstat(fdt, &dirt) < 0)
			fprint(2, "cp: warning: can't wstat %s: %r\n", to);
	}
	free(dirb);
	close(fdf);
	close(fdt);
}

int
copy1(int fdf, int fdt, char *from, char *to)
{
	char *buf;
	long n, n1, rcount;
	int rv;
	char err[ERRMAX];

	buf = malloc(mtu);
	/* clear any residual error */
	err[0] = '\0';
	errstr(err, ERRMAX);
	rv = 0;
	for(rcount=0;; rcount++) {
		n = read(fdf, buf, mtu);
		if(n <= 0)
			break;
		n1 = write(fdt, buf, n);
		if(n1 != n) {
			fprint(2, "cp: error writing %s: %r\n", to);
			failed = 1;
			rv = -1;
			break;
		}
	}
	if(n < 0) {
		fprint(2, "cp: error reading %s: %r\n", from);
		failed = 1;
		rv = -1;
	}
	free(buf);
	return rv;
}
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