On 02/16/2018 02:59 PM, H. Peter Anvin wrote: > On 02/16/18 12:33, Taras Kondratiuk wrote: >> Many of the Linux security/integrity features are dependent on file >> metadata, stored as extended attributes (xattrs), for making decisions. >> These features need to be initialized during initcall and enabled as >> early as possible for complete security coverage. >> >> Initramfs (tmpfs) supports xattrs, but newc CPIO archive format does not >> support including them into the archive. >> >> This patch describes "extended" newc format (newcx) that is based on >> newc and has following changes: >> - extended attributes support >> - increased size of filesize to support files >4GB >> - increased mtime field size to have 64 bits of seconds and added a >> field for nanoseconds >> - removed unused checksum field >> > > If you are going to implement a new, non-backwards-compatible format, > you shouldn't replicate the mistakes of the current format. Specifically: So rather than make minimal changes to the existing format and continue to support the existing format (sharing as much code as possible), you recommend gratuitous aesthetic changes? > 1. The use of ASCII-encoded fixed-length numbers is an idiotic legacy > from an era before there were any portable way of dealing with numbers > with prespecified endianness. It lets encoders and decoders easily share code with the existing cpio format, which we still intend to be able to read and write. > If you are going to use ASCII, make them > delimited so that they don't have fixed limits, or just use binary. When it's gzipped this accomplishes what? (Other than being gratuitously different from the previous iteration?) > The cpio header isn't fixed size, so that argument goes away, in fact > the only way to determine the end of the header is to scan forward. > > 2. Alignment sensitivity! Because there is no header length > information, the above scan tells you where the header ends, but there > is padding before the data, and the size of that padding is only defined > by alignment. Again, these are minimal changes to the existing cpio format. You're complaining about _cpio_, and that the new stuff isn't _different_ enough from it. > 3. Inband encoding of EOF: if you actually have a filename "TRAILER!!!" > you have problems. Been there, done that: http://lkml.iu.edu/hypermail/linux/kernel/1801.3/01791.html > But first, before you define a whole new format for which no tools exist > (you will have to work with the maintainers of the GNU tools to add > support) No, he's been working with the maintainer of toybox to add support (for about a year now), which gets him the Android command line. And the kernel has its own built-in tool to generate cpio images anyway. Why would anyone care what the GNU project thinks? > you should see how complex it would be to support the POSIX > tar/pax format, That argument was had (at length) when initramfs went in over a decade ago. There are links in Documentation/filesystems/ramfs-rootfs-initramfs.txt to the mailing list entries about it. > which already has all the features you are seeking, and > by now is well-supported. So... tar wasn't well-supported 15 years ago? (Hasn't the kernel source always been distributed via tarball back since 0.0.1?) You're suggesting having a whole second codepath that shares no code with the existing cpio extractor. Are you suggesting abandoning support for the existing initramfs.cpio.gz file format? Rob -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
