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Date:      Wed, 18 Jan 2006 19:43:21 -0500
From:      Kris Kennaway <kris@obsecurity.org>
To:        "Shin,Hee-Sub" <heesub.shin@samsung.com>
Cc:        freebsd-questions@FreeBSD.org
Subject:   Re: About VFS locking strategy...
Message-ID:  <20060119004321.GA58284@xor.obsecurity.org>
In-Reply-To: <000001c61c89$0da481a0$19a5580a@swcenter.sec.samsung.co.kr>
References:  <000001c61c89$0da481a0$19a5580a@swcenter.sec.samsung.co.kr>

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On Thu, Jan 19, 2006 at 08:43:55AM +0900, Shin,Hee-Sub wrote:
> Hi all.=20
>=20
> =20
>=20
> I'm speluking with source code of FreeBSD now, comparing VFS of FBSD and
> the linux's.=20
>=20
> =20
>=20
> I have a question related with concurrent accesses to the file system. It
> is seemed that VFS locks and unlocks each VNODEs before calling VNODE OPS
> provided by underlying FS. For example, it calls vn_lock(vp, ...) before
> jumps to VOP_READ() in vn_read().=20
>=20
> =20
>=20
> WindowsCE kernel also has a component that is responsible for switching FS
> requests to appropriate file-system underlying and similar with VFS of ma=
ny
> UNIX variants, but it's not perfectly same. In WindowsCE world, file syst=
em
> driver code can be called on re-entry and file system programmer should
> keep this in mind. The manager does not manage any synchronization proble=
ms
> that can be occurred when multiple threads access to the file system. It
> has only a few locks for protecting its own data structures.=20
>=20
> =20
>=20
> How does it manage synchronization problems in the VFS of FreeBSD?=20
>=20
> =20
>=20
> Please give me a detailed description about lock strategy the FreeBSD use=
s.=20

This question might be too general to get any replies, but it would
still be better asked on fs@ or hackers@.

Kris
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