packfile: recover when a multi-pack-index names a removed pack A geometric repack writes a new pack and multi-pack-index and then deletes the packs the new one subsumes. A process still using the previous MIDX keeps seeing a removed pack listed as the owner of some objects. Since a MIDX attributes each object to exactly one pack, such an object is served only through its recorded owner; if that owner was just removed, find_pack_entry() cannot serve it -- the MIDX lookup routes to the missing pack, and the regular pack fallback deliberately skips every MIDX-covered pack, so a surviving copy in another covered pack (e.g. a kept base pack) is never consulted. Unlike the ordinary "a pack's .idx is mapped but its .pack is gone" race, the second read does not rescue us. Reloading the on-disk pack set does not reload the borrowed, cached MIDX (freeing it under the code that caches the "struct multi_pack_index *" would be a use-after-free), so the stale MIDX keeps routing to the removed pack and the surviving copy stays hidden behind the covered-pack skip. cat-file, rev-list and pack-objects can thus all spuriously fail with "unable to read object". Teach find_pack_entry() to recover. The MIDX lookup now returns a tri-state, distinguishing an object absent from the MIDX from one it owns via a pack that can no longer be opened; in the latter case, once the regular fallback has also missed, scan the MIDX's packs directly for a surviving copy. Because the return value is no longer a boolean, rename fill_midx_entry() to midx_fill_entry() so callers must reckon with the new enum rather than silently treat MIDX_FILL_OWNER_UNAVAILABLE as a hit. Do the scan only on the second read (OBJECT_INFO_SECOND_READ): by then the cheaper on-disk reload has run, so an object merely relocated into a new (uncovered) pack has already been found by the regular fallback, and only a genuine hidden duplicate reaches the rescan. A QUICK caller that skips the second read simply accepts the false negative, as QUICK is designed to. Reloading the stale MIDX would be a more complete fix but is much more involved (the borrowers above need proper invalidation), so leave that for later. Assisted-by: Claude Opus 4.8 & GPT-5.6 Sol Helped-by: Jeff King <peff@peff.net> Signed-off-by: Elijah Newren <newren@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Git is a fast, scalable, distributed revision control system with an unusually rich command set that provides both high-level operations and full access to internals.
Git is an Open Source project covered by the GNU General Public License version 2 (some parts of it are under different licenses, compatible with the GPLv2). It was originally written by Linus Torvalds with help of a group of hackers around the net.
Please read the file INSTALL for installation instructions.
Many Git online resources are accessible from https://git-scm.com/ including full documentation and Git related tools.
See Documentation/gittutorial.adoc to get started, then see Documentation/giteveryday.adoc for a useful minimum set of commands, and Documentation/git-<commandname>.adoc for documentation of each command. If git has been correctly installed, then the tutorial can also be read with man gittutorial or git help tutorial, and the documentation of each command with man git-<commandname> or git help <commandname>.
CVS users may also want to read Documentation/gitcvs-migration.adoc (man gitcvs-migration or git help cvs-migration if git is installed).
The user discussion and development of Git take place on the Git mailing list -- everyone is welcome to post bug reports, feature requests, comments and patches to git@vger.kernel.org (read Documentation/SubmittingPatches for instructions on patch submission and Documentation/CodingGuidelines).
Those wishing to help with error message, usage and informational message string translations (localization l10) should see po/README.md (a po file is a Portable Object file that holds the translations).
To subscribe to the list, send an email to git+subscribe@vger.kernel.org (see https://subspace.kernel.org/subscribing.html for details). The mailing list archives are available at https://lore.kernel.org/git/, https://marc.info/?l=git and other archival sites.
Issues which are security relevant should be disclosed privately to the Git Security mailing list git-security@googlegroups.com.
The maintainer frequently sends the “What's cooking” reports that list the current status of various development topics to the mailing list. The discussion following them give a good reference for project status, development direction and remaining tasks.
The name “git” was given by Linus Torvalds when he wrote the very first version. He described the tool as “the stupid content tracker” and the name as (depending on your mood):