From: Philip Oakley Date: Sun, 04 Dec 2016 11:23:02 GMT Subject: Re: Git v2.11.0 breaks max depth nested alternates Message-ID: <49DE271A91214D6DADBD4DE667A1659B@PhilipOakley> In-Reply-To: From: "Kyle J. McKay" Sent: Sunday, December 04, 2016 12:24 AM > The recent addition of pre-receive quarantining breaks nested > alternates that are already at the maximum alternates nesting depth. > > In the file sha1_file.c in the function link_alt_odb_entries we have > this: > > > if (depth > 5) { > > error("%s: ignoring alternate object stores, nesting too deep.", > > relative_base); > > return; > > } > > When the incoming quarantine takes place the current objects directory > is demoted to an alternate thereby increasing its depth (and any > alternates it references) by one and causing any object store that was > previously at the maximum nesting depth to be ignored courtesy of the > above hard-coded maximum depth. > > If the incoming push happens to need access to some of those objects > to perhaps "--fix-thin" its pack it will crash and burn. > > Originally I was not going to include a patch to fix this, but simply > suggest that the expeditious fix is to just allow one additional > alternates nesting depth level during quarantine operations. > > However, it was so simple, I have included the patch below :) > > I have verified that where a push with Git v2.10.2 succeeds and a push > with Git v2.11.0 to the same repository fails because of this problem > that the below patch does indeed correct the issue and allow the push > to succeed. > > Cheers, > > Kyle > > -- 8< -- > Subject: [PATCH] receive-pack: increase max alternates depth during > quarantine > > Ever since 722ff7f876 (receive-pack: quarantine objects until > pre-receive accepts, 2016-10-03, v2.11.0), Git has been quarantining > objects and packs received during an incoming push into a separate > objects directory and using the alternates mechanism to make them > available until they are either accepted and moved into the main > objects directory or rejected and discarded. Is there a step here that after the accepted/rejected stage, it should then decrement the limit back to its original value. The problem description suggests that might be the case. -- Philip > > Unfortunately this has the side effect of increasing the alternates > nesting depth level by one for all pre-existing alternates. > > If a repository is already at the maximum alternates nesting depth, > then this quarantining operation can temporarily push it over making > the incoming push fail. > > To prevent the failure we simply increase the allowed alternates > nesting depth by one whenever a quarantine operation is in effect. > > Signed-off-by: Kyle J. McKay > --- > > Notes: > Some alternates nesting depth background: > > If base/fork0/fork1/fork2/fork3/fork4/fork5 represents > seven git repositories where base.git has no alternates, > fork0.git has base.git as an alternate, fork1.git has > fork0.git as an alternate and so on where fork5.git has > only fork4.git as an alternate, then fork5.git is at > the maximum allowed depth of 5. git fsck --strict --full > works without complaint on fork5.git. > > However, in base/fork0/fork1/fork2/fork3/fork4/fork5/fork6, > an fsck --strict --full of fork6.git will generate complaints > and any objects/packs present in base.git will be ignored. > > cache.h | 1 + > common-main.c | 3 +++ > environment.c | 1 + > sha1_file.c | 2 +- > 4 files changed, 6 insertions(+), 1 deletion(-) > > diff --git a/cache.h b/cache.h > index a50a61a1..25c17c29 100644 > --- a/cache.h > +++ b/cache.h > @@ -676,6 +676,7 @@ extern size_t packed_git_limit; > extern size_t delta_base_cache_limit; > extern unsigned long big_file_threshold; > extern unsigned long pack_size_limit_cfg; > +extern int alt_odb_max_depth; > > /* > * Accessors for the core.sharedrepository config which lazy-load the > value > diff --git a/common-main.c b/common-main.c > index c654f955..9f747491 100644 > --- a/common-main.c > +++ b/common-main.c > @@ -37,5 +37,8 @@ int main(int argc, const char **argv) > > restore_sigpipe_to_default(); > > + if (getenv(GIT_QUARANTINE_ENVIRONMENT)) > + alt_odb_max_depth++; > + > return cmd_main(argc, argv); > } > diff --git a/environment.c b/environment.c > index 0935ec69..32e11f70 100644 > --- a/environment.c > +++ b/environment.c > @@ -64,6 +64,7 @@ int merge_log_config = -1; > int precomposed_unicode = -1; /* see probe_utf8_pathname_composition() */ > unsigned long pack_size_limit_cfg; > enum hide_dotfiles_type hide_dotfiles = HIDE_DOTFILES_DOTGITONLY; > +int alt_odb_max_depth = 5; > > #ifndef PROTECT_HFS_DEFAULT > #define PROTECT_HFS_DEFAULT 0 > diff --git a/sha1_file.c b/sha1_file.c > index 9c86d192..15b8432e 100644 > --- a/sha1_file.c > +++ b/sha1_file.c > @@ -337,7 +337,7 @@ static void link_alt_odb_entries(const char *alt, int > len, int sep, > int i; > struct strbuf objdirbuf = STRBUF_INIT; > > - if (depth > 5) { > + if (depth > alt_odb_max_depth) { > error("%s: ignoring alternate object stores, nesting too deep.", > relative_base); > return; > --- >