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Date: Tue, 25 Aug 2009 20:04:48 -0400
Message-ID: <3aaafc130908251704r290afa5fsa3833c20db97bbbc@mail.gmail.com>
From: "J.R. Mauro" <jrm8005@gmail.com>
To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
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Subject: Re: [9fans] Possible bug in p9p venti?
Topicbox-Message-UUID: 52cd6880-ead5-11e9-9d60-3106f5b1d025

On Sun, Aug 23, 2009 at 11:10 AM, Venkatesh Srinivas<me@acm.jhu.edu> wrote:
> Hi,
>
> I think I've found a bug in p9p's Venti, if anyone were to take a look
> at this code or tell me if I'm on the right track, it'd be pretty
> neat.
>
> When trying to start Venti on a FreeBSD 8-BETA2 system and a ZFS
> filesystem, we got this error:
> 2009/0822 23:12:30 venti: conf...
> 2009/0822 23:12:30 err 4: read arena0 offset 0x60000 count 65536 buf
> 803f20000 returned 65536: No such file or directory
> 2009/0822 23:12:30 err 4: can't read arena0: read arena0 offset
> 0x60000 count 65536 buf 803f20000 returned 65536: No such file or
> directory
> venti: can't init server: can't initialize venti: arena0: can't read
> arena0: read arena0 offset 0x60000 count 65536 buf 803f20000 returned
> 65536: No such
>
> In venti/srv/part.c:325, opsize is clamped at MaxIo, which is 64KB by
> default. Later, on :329, we issue a pread for opsize bytes from our
> partition, but check that the read returned some multiple of
> blocksize. (Blocksize comes from part->fsblocksize, which is gotten by
> fstatfs()'s .f_bsize on unix.) This is a problem when MaxIo <
> blocksize ; on ZFS on FreeBSD, f_bsize =3D 128K.
>
> A workaround is to clamp fsblocksize at MaxIo as well:
> --- part.c.orig 2009-08-23 11:07:56.000000000 -0400
> +++ part.c =A02009-08-23 11:06:46.000000000 -0400
> @@ -166,6 +166,9 @@
> =A0 =A0 =A0 =A0 =A0 =A0part->fsblocksize =3D sfs.f_bsize;
> =A0 =A0}
> =A0#endif
> +
> + =A0 part->fsblocksize =3D min(part->fsblocksize, MaxIo);
> +
> =A0 =A0if(subname && findsubpart(part, subname) < 0){
> =A0 =A0 =A0 =A0werrstr("cannot find subpartition %s", subname);
> =A0 =A0 =A0 =A0freepart(part);
>
> Thanks,
> -- vs
>
>

Any chance this is related to the issues we discussed on #plan9?