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Hash: SHA1 |
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Tiziano Müller wrote: |
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> Am Montag, den 02.02.2009, 12:34 -0800 schrieb Zac Medico: |
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>> For the digest format, I suggest that we use the leftmost 10 |
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>> hexadecimal digits of the SHA-1 digest. The rationale for limiting |
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>> it to 10 digits (out of 40) is to save space. Due to the avalanche |
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>> effect [2], 10 digits should be sufficient to ensure that problems |
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>> resulting from hash collisions are extremely unlikely. |
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> I'd recommend to prefix the digest with a "{TYPE}" (like for hashed |
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> passwords) to be able to change the digest algorithm as needed |
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> (especially in regards to the current SHA successor competition). |
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> This allows a future package manager which might use SHA-3 for hashing |
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> (once it's released) to still check old digests. Furthermore it would |
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> allow for easier transition and only needs a definition of allowed |
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> hashes instead of a specific one. |
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I like that idea. That way it's not necessary to bump the EAPI in |
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order to change the hash function. So, a typical DIGESTS value might |
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look like this: |
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|
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SHA1 02021be38b a28b191904 3992945426 6ec21b29a3 |
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|
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>> The primary reason to use a digest for cache validation instead of a |
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>> timestamp is that it allows the cache validation mechanism to work |
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>> even if the tree is distributed with a protocol that does not |
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>> preserve timestamps, such as git or subversion. This would make it |
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> Well, usually you don't keep intermediate or generated files in a VCS, |
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> so why the metadata? |
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|
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People who distribute overlays commonly ask if it's possible to |
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distribute metadata cache with the overlay. Using a format that |
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doesn't rely on timestamps will allow them to distribute metadata |
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cache using their existing infrastructure, which is typically git or |
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subversion. In addition to overlays, it would also be useful for |
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forks of the entire gentoo tree, such as the funtoo tree [1]. |
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[1] http://github.com/funtoo/portage/tree/master |
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- -- |
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Thanks, |
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Zac |
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iEYEARECAAYFAkmOF+UACgkQ/ejvha5XGaPSyQCg7kVF3S1z4G+7pXOrLBB1Pu77 |
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Y5cAnj60bGSww8SLfcqhHmk1voKwm20+ |
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=PmlJ |
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