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update doc formatting

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Motiejus Jakštys 2021-05-31 21:44:17 +03:00
parent 12d13c5c98
commit ccdea382b6
1 changed files with 26 additions and 23 deletions
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49
rootfs/doc.go
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@ -5,30 +5,31 @@
// It will also reasonably process those files.
//
// == Non-directory will be copied only once ==
//
// A non-directory will be copied only once, only from within it's past
// occurrence. I.e. if file /a/b was found in layers 0 and 2, only the file
// from layer 2 will be used.
// Directories will always be copied, even if there are duplicates. This is
// to avoid a situation like this:
// layer0:
// - ./dir/
// - ./dir/file
// ./dir/
// ./dir/file
// layer1:
// - ./dir/
// - ./dir/file
// ./dir/
// ./dir/file
// In theory, the directory from layer 1 takes precedence, so a tarball like
// this could be created:
// - ./dir/ (from layer1)
// - ./dir/file1 (from layer1)
// ./dir/ (from layer1)
// ./dir/file1 (from layer1)
// However, imagine the following:
// layer0:
// - ./dir/
// - ./dir/file1
// ./dir/
// ./dir/file1
// layer1:
// - ./dir/
// ./dir/
// Then the resulting tarball would have:
// - ./dir/file1 (from layer1)
// - ./dir/ (from layer0)
// ./dir/file1 (from layer1)
// ./dir/ (from layer0)
// Which would mean `untar` would try to untar a file to a directory which
// was not yet created. Therefore directories will be copied to the resulting
// tar in the order they appear in the layers.
@ -44,21 +45,22 @@
//
// From mount.aufs(8)[1]:
//
// The whiteout is for hiding files on lower branches. Also it is applied to
// stop readdir going lower branches. The latter case is called ‘opaque
// directory.’ Any whiteout is an empty file, it means whiteout is just an
// mark. In the case of hiding lower files, the name of whiteout is
// ‘.wh.<filename>.’ And in the case of stopping readdir, the name is
// ‘.wh..wh..opq’. All whiteouts are hardlinked, including ‘<writable branch
// top dir>/.wh..wh.aufs`.
// The whiteout is for hiding files on lower branches. Also it is applied to
// stop readdir going lower branches. The latter case is called ‘opaque
// directory.’ Any whiteout is an empty file, it means whiteout is just an
// mark. In the case of hiding lower files, the name of whiteout is
// ‘.wh.<filename>.’ And in the case of stopping readdir, the name is
// ‘.wh..wh..opq’. All whiteouts are hardlinked, including ‘<writable branch
// top dir>/.wh..wh.aufs`.
//
// My interpretation:
// - a file/hardlink called `.wh..wh..opq` means that directory contents from
//
// 1. a file/hardlink called `.wh..wh..opq` means that directory contents from
// the layers below the mentioned file should be ignored. Higher layers may add
// files on top.
// * Ambiguity: should the directory from the lower layers be removed? I am
// assuming yes, but this assumptions is baseless.
// - if file/hardlink `.wh.([^/]+)` is found, $1 should be deleted from the
// files on top. Ambiguity: should the directory from the lower layers be
// removed? I am assuming yes, but this assumptions is baseless.
//
// 2. if file/hardlink `.wh.([^/]+)` is found, $1 should be deleted from the
// current and lower layers.
//
// Note: these may be regular files in practice. So this implementation will
@ -71,5 +73,6 @@
// problems reading it[2].
//
// [1]: https://manpages.debian.org/unstable/aufs-tools/mount.aufs.8.en.html
//
// [2]: https://mgorny.pl/articles/portability-of-tar-features.html
package rootfs