kernel/git - git - PowerEL Git System

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Author	SHA1	Message	Date
Jeff King	067fbd4105	introduce "preciousObjects" repository extension If this extension is used in a repository, then no operations should run which may drop objects from the object storage. This can be useful if you are sharing that storage with other repositories whose refs you cannot see. For instance, if you do: $ git clone -s parent child $ git -C parent config extensions.preciousObjects true $ git -C parent config core.repositoryformatversion 1 you now have additional safety when running git in the parent repository. Prunes and repacks will bail with an error, and `git gc` will skip those operations (it will continue to pack refs and do other non-object operations). Older versions of git, when run in the repository, will fail on every operation. Note that we do not set the preciousObjects extension by default when doing a "clone -s", as doing so breaks backwards compatibility. It is a decision the user should make explicitly. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>	10 years ago
Jeff King	00a09d57eb	introduce "extensions" form of core.repositoryformatversion Normally we try to avoid bumps of the whole-repository core.repositoryformatversion field. However, it is unavoidable if we want to safely change certain aspects of git in a backwards-incompatible way (e.g., modifying the set of ref tips that we must traverse to generate a list of unreachable, safe-to-prune objects). If we were to bump the repository version for every such change, then any implementation understanding version `X` would also have to understand `X-1`, `X-2`, and so forth, even though the incompatibilities may be in orthogonal parts of the system, and there is otherwise no reason we cannot implement one without the other (or more importantly, that the user cannot choose to use one feature without the other, weighing the tradeoff in compatibility only for that particular feature). This patch documents the existing repositoryformatversion strategy and introduces a new format, "1", which lets a repository specify that it must run with an arbitrary set of extensions. This can be used, for example: - to inform git that the objects should not be pruned based only on the reachability of the ref tips (e.g, because it has "clone --shared" children) - that the refs are stored in a format besides the usual "refs" and "packed-refs" directories Because we bump to format "1", and because format "1" requires that a running git knows about any extensions mentioned, we know that older versions of the code will not do something dangerous when confronted with these new formats. For example, if the user chooses to use database storage for refs, they may set the "extensions.refbackend" config to "db". Older versions of git will not understand format "1" and bail. Versions of git which understand "1" but do not know about "refbackend", or which know about "refbackend" but not about the "db" backend, will refuse to run. This is annoying, of course, but much better than the alternative of claiming that there are no refs in the repository, or writing to a location that other implementations will not read. Note that we are only defining the rules for format 1 here. We do not ever write format 1 ourselves; it is a tool that is meant to be used by users and future extensions to provide safety with older implementations. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>	10 years ago

Author

SHA1

Message

Date

Jeff King

067fbd4105

introduce "preciousObjects" repository extension

If this extension is used in a repository, then no
operations should run which may drop objects from the object
storage. This can be useful if you are sharing that storage
with other repositories whose refs you cannot see.

For instance, if you do:

  $ git clone -s parent child
  $ git -C parent config extensions.preciousObjects true
  $ git -C parent config core.repositoryformatversion 1

you now have additional safety when running git in the
parent repository. Prunes and repacks will bail with an
error, and `git gc` will skip those operations (it will
continue to pack refs and do other non-object operations).
Older versions of git, when run in the repository, will
fail on every operation.

Note that we do not set the preciousObjects extension by
default when doing a "clone -s", as doing so breaks
backwards compatibility. It is a decision the user should
make explicitly.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

10 years ago

Jeff King

00a09d57eb

introduce "extensions" form of core.repositoryformatversion

Normally we try to avoid bumps of the whole-repository
core.repositoryformatversion field. However, it is
unavoidable if we want to safely change certain aspects of
git in a backwards-incompatible way (e.g., modifying the set
of ref tips that we must traverse to generate a list of
unreachable, safe-to-prune objects).

If we were to bump the repository version for every such
change, then any implementation understanding version `X`
would also have to understand `X-1`, `X-2`, and so forth,
even though the incompatibilities may be in orthogonal parts
of the system, and there is otherwise no reason we cannot
implement one without the other (or more importantly, that
the user cannot choose to use one feature without the other,
weighing the tradeoff in compatibility only for that
particular feature).

This patch documents the existing repositoryformatversion
strategy and introduces a new format, "1", which lets a
repository specify that it must run with an arbitrary set of
extensions. This can be used, for example:

 - to inform git that the objects should not be pruned based
   only on the reachability of the ref tips (e.g, because it
   has "clone --shared" children)

 - that the refs are stored in a format besides the usual
   "refs" and "packed-refs" directories

Because we bump to format "1", and because format "1"
requires that a running git knows about any extensions
mentioned, we know that older versions of the code will not
do something dangerous when confronted with these new
formats.

For example, if the user chooses to use database storage for
refs, they may set the "extensions.refbackend" config to
"db". Older versions of git will not understand format "1"
and bail. Versions of git which understand "1" but do not
know about "refbackend", or which know about "refbackend"
but not about the "db" backend, will refuse to run. This is
annoying, of course, but much better than the alternative of
claiming that there are no refs in the repository, or
writing to a location that other implementations will not
read.

Note that we are only defining the rules for format 1 here.
We do not ever write format 1 ourselves; it is a tool that
is meant to be used by users and future extensions to
provide safety with older implementations.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

10 years ago

2 Commits (3206b6bdf6c261633b3712b7549b794aa39a5169)