On Thu, 2 Aug 2007 12:05:36 -0400 "J. Bruce Fields" <[EMAIL PROTECTED]> wrote:
> On Thu, Aug 02, 2007 at 11:32:55AM -0400, Jeff Layton wrote: > > On Tue, 31 Jul 2007 10:48:24 -0400 > > "J. Bruce Fields" <[EMAIL PROTECTED]> wrote: > > > That's an interesting problem. Thanks for the report! > > > > > > I don't believe that long comma-delimited string actually has any > > > meaning to the kernel--as far as the kernel is concerned, it's just an > > > opaque object that will be passed back to mountd later (along with a > > > path name) to get export options. > > > > > > So I suppose that string could be replaced by a hash, or maybe even just > > > by the ip address of the particular host--the disadvantage to the latter > > > being that it would require the kernel to keep a separate export for > > > each client address. > > > > I started having a look at this today. The original patches that I > > proposed to clean up the rmtab a few months ago also eliminated this > > comma-delimited string. Neil had valid objections to it at the time, > > but if we switched to using the IP address as a cache key like Bruce > > describes then doing that becomes more reasonable. > > > > The only downside I see is the one Bruce points out -- the size of > > the kernel export cache would increase. I don't have a feel for whether > > this is a show stopper, however. > > Yeah, there might be some risk of solving that problem at the expense of > people with tons of clients all matching *.example.com. The actual > export objects are actually pretty small--68 bytes, last I checked? > You'd also need two upcalls to mountd per client (for ip address and > export, as opposed to just ip address). I don't know what other costs > there might be. > Yeah, that could make using the ipaddr too costly... > What about the idea of hashing the comma-delimited list and passing > that? You'd want hash large enough to be collision-free--might as well > use some cryptographic hash, I guess, though it may be mild overkill. > Is there any reason why that wouldn't work? > Hashing would certainly work. The only issue though is that this doesn't take care of the second problem, which is that NFSCLNT_IDMAX is too small for some environments. So this change would need to be coupled with an increase in this hardcoded value, change m_hostname to be dynamically allocated, or change the comma-delimited string to some other scheme entirely (maybe a linked list of some sort?). As far as the hashing scheme, I guess we could use the glibc crypt() routine that does md5 hashing. I'd like to avoid adding dependencies on new libs if possible. > Could you remind me what problems you were trying to fix with your rmtab > cleanup? > Those patches were really intended to get showmount -a to look correct. My first pass at it changed the m_hostname field to hold an actual hostname, got rid of the comma-separated strings and just had mountd do repeated calls to client_check to check the host's validity. This was problematic though with a multi-homed client though since the export table key then became a hostname rather than the comma-delimited string and more than 1 ip addr could resolve to it. If we use the ipaddr as a key, then this problem goes away, but then we have the other issues you've detailed above. -- Jeff Layton <[EMAIL PROTECTED]> - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
