* Luigi Rizzo <[EMAIL PROTECTED]> [011023 13:50] wrote: > On Tue, Oct 23, 2001 at 01:28:13PM -0500, Alfred Perlstein wrote: > ... > > > In the mbuf code, M_LEADINGSPACE always returns 0 when M_EXT is > > > set, instead of calling the second part of M_WRITABLE to check > > > whether there is a chance of writing into the cluster. This means > ... > > I've seen this brought up before, this is not what you want to > > do otherwise you risk corrupting EXT data. The right thing to > > do is have the people allocating writable EXT bufs mark them > > as such. Other EXT type buffers such as sendfile bufs can not > > be written to no matter what the sharecount is. > > Actually, the BSD code works the other way around: > > * standard EXT bufs as returned by MCLGET _are_ writable if > m_ext.ext_free == NULL and their refcnt is 1 (they _must_ be, > otherwise we would have errors when m_free() decides to > dispose of a cluster, which is a form of writing), > > and > > * people allocating "other EXT type" implicitly mark the buffer > as not-writable by setting m_ext.ext_free to the proper routine. > This is certainly what the sendfile bufs that you mentioned do. > > M_WRITABLE (used in the patch i proposed) does exactly the checks > that you do when you m_free() a cluster. If this is wrong, then > m_free() is broken! > > Am i missing something else ?
Yes, you're right, I was mistaken in my paranioa, however you're missing the fact that one may want to allocate an EXT buf and still have it writeable. I like your patch, it's a good idea, go for it. -Alfred To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-net" in the body of the message
