Yeah, what James said.
That said, in most cases the mount/unmount penalty is not bad, because
in cases where it was, I did some caching to make it less onerous.
Cases in point include JFFS2, where mount is inherently horrible, so I
cache the result of scanning the whole NAND surface, and the network,
where I cache the DHCP result.
If you have problems, tell me. My intention is that subsequent mounts
should be fast enough.
On 9/21/2011 11:39 AM, James Cameron wrote:
On Wed, Sep 21, 2011 at 04:21:42PM +0100, Daniel Drake wrote:
One lingering question is how OFW deals with mounting/unmounting.
I know that some words (in some contexts?) cause the disk to be
mounted, then the command to be executed, then the disk unmounted.
Every open effectively causes a device initialisation and read of
filesystem metadata. It is one reason why external SD is so slow for
multiple operations on XO-1.5; there's a coded delay for allowing the
card supply rail to fall far enough for the card to reset.
But OpenFirmware isn't doing anything else, so the operations tend to be
reasonably fast.
Will the previously attached code cause a lot of mounts/unmounts?
Yes. bundle-present? place-ramdisk ?ofw-reflash $file-exists?
I'm particularly worried that it would slow down boot noticably. The
ideal of course is that it only gets mounted once, before this code
executes.
Measure it. In stages if necessary. Enclose sections in t( )t pairs.
e.g.
" last:\boot\vmlinuz" 2dup
t( $file-exists? ." time: vmlinuz existence" )t cr
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