On Wed, Feb 16, 2011 at 11:03:15AM +0100, Thorsten Glaser wrote: > why not “just” write something that walks like an sbuild, > quacks like an sbuild, and calls cowbuilder? > > This would solve all the problems with tearing down pak- > kage installation etc. > > … except #363193 (I think pbuilder too needs some love, > or team maintenance).
cowbuilder has one major flaw: the copy-on-write is implemented by LD_PRELOAD, as a shared library copied from the host system. This precludes the build environment from having a glibc incompatible with the host, since it would break the copy-on-write functionality. Additionally, the LD_PRELOAD symbol coverage may become outdated as glibc adds new symbols, resulting in some actions overwriting the base environment. Example: the new openat/mkdirat variants of the basic system calls. These also need preloading. And it will break every time a new symbol needing preloading is added. I did look at it in detail a year or so back, but it's really too fragile to use long-term. It's not that it doesn't work, it's that continued reliability is not guaranteed. sbuild has the ability to host alternative architectures in the chroot; currently 32/64 bit versions of the same arch e.g. i386/amd64. LD_PRELOAD would break here. Soon, we will also gain the ability (via schroot) of using qemu-$arch-static and binfmt-misc to run binaries from any arbitrary arch inside the chroot to do builds for non-native architectures; here we also can't do copy-on-write. sbuild itself relies entirely upon schroot to do its virtualisation. cowbuilder-like support could potentially be added to schroot to give sbuild this functinality, but it would require some refactoring of schroot to permit this. I can put it on my TODO list, but I'm afraid it won't be a priority item. The existing lvm-snapshot support is both fast and (bar kernel bugs) completely reliable WRT data being genuinely copy-on-write. We now have btrfs snapshot support when is even quicker to create snapshots, but currently performs badly with dpkg; hopefully this will be addressed by dpkg now squeeze is out. While these require setup by the sysadmin, they both have the copy-on-write guarantees we need. Regards, Roger -- .''`. Roger Leigh : :' : Debian GNU/Linux http://people.debian.org/~rleigh/ `. `' Printing on GNU/Linux? http://gutenprint.sourceforge.net/ `- GPG Public Key: 0x25BFB848 Please GPG sign your mail.
signature.asc
Description: Digital signature
