On Thu, Apr 19, 2007 at 09:43:50AM -0700, Linus Torvalds wrote:
> On Thu, 19 Apr 2007, Johannes Schindelin wrote:
> > Hmm. However, I have to say that cogito serves/d another purpose quite
> > well: Look at what came from cogito into git. Loads of useful
> > enhancements. So, I really have to point to "at this stage", because that
> > sure was not true 18 months ago.
>
> Absolutely. I think there are still some pieces of cogito that we might
> want to migrate into git too, although they're fairly esoteric (ie the
> whole history rewriting thing). And I think we still have some places
I actually have a fairly simple history rewriting script (written in python)
that I used when I converted some CVS archives to git. It is really intended
for such an initial import and history cleanup case so it doesn't deal with
reflogs and such.
Basic workflow I used is,
- Import CVS archive into a git repository
- Use gitk + the grafts file to clean up history as much as feasible
- Run git-rewrite-history.py which will
- write out new commit objects with the corrected set of parents
- copy existing refs to .git/newrefs, pointing them at the new commits.
- start gitk --all to see the tree before the rewrite.
- mv .git/refs .git/oldrefs ; mv .git/newrefs .git/refs
- start a second gitk --all to see the tree after the rewrite.
- compare gitk output to check if everything matches up.
- run git repack/prune/gc to get rid of the old commits, or clone the repo.
Jan
--8<-----------------------------------------------------------------------
#!/usr/bin/python
import os, sys
def git_write_object(type, blob):
stdin, stdout = os.popen2("git-hash-object -t %s -w --stdin" % type)
stdin.write(blob)
stdin.close()
return stdout.readline().strip()
def git_commits(branch):
f = os.popen('git-rev-list --parents --header --topo-order %s' % branch)
buf = ''
while 1:
buf = buf + f.read(4096)
if not buf: break
if not '\0' in buf: continue
commit, buf = buf.split('\0', 1)
yield Commit(commit)
def git_update_ref(name, hash):
os.system('git-update-ref "%s" "%s"' % (name, hash))
grafts = []
pending = []
rewriteable = []
remap = {}
todo = 0
class Commit:
def __init__(self, commit):
global grafts
lines = commit.split('\n')
parts = lines.pop(0).split()
self.hash, self.parents = parts[0], parts[1:]
self.tree = lines.pop(0)
parents = []
while lines[0][:7] == 'parent ':
parents = parents + lines.pop(0).split()[1:]
if parents != self.parents:
grafts.append(self.hash)
commit = []
while 1:
line = lines.pop(0)
commit.append(line)
if not line: break
for line in lines:
commit.append(line[4:])
self.commit = '\n'.join(commit)
self.wait = 0
self.children = []
def mark(self):
global todo, pending
self.wait = self.wait + 1
if self.wait == 1:
todo = todo + 1
for child in self.children:
pending.append(child.hash)
def pick(self):
global rewriteable
self.wait = self.wait - 1
if not self.wait:
rewriteable.append(self)
def fixup(self, old_hash, new_hash):
i = self.parents.index(old_hash)
self.parents[i] = new_hash
self.pick()
def rehash(self):
global todo, remap
todo = todo - 1
blob = self.tree + '\n'
for parent in self.parents:
blob = blob + 'parent %s\n' % parent
blob = blob + self.commit
new_hash = git_write_object('commit', blob)
remap[self.hash] = new_hash
for child in self.children:
child.fixup(self.hash, new_hash)
print "Reading commits... ",
commits = {}
for commit in git_commits('--all'):
commits[commit.hash] = commit
print "read %d commits, found %d grafts" % (len(commits), len(grafts))
print "Setting up reverse linkage"
for commit in commits.values():
for parent in commit.parents:
commits[parent].children.append(commit)
print "Propagating graft information... ",
# first mark all commits that will have to be rewritten.
for commit in grafts:
commits[commit].mark()
for commit in pending:
commits[commit].mark()
# pick those commits that do not depend on any earlier rewrites
for commit in grafts:
commits[commit].pick()
print "%d commits need to be rewritten" % todo
print "Rewriting commits... "
while rewriteable:
print "\rrewriting %5d/%5d commits" % (len(rewriteable), todo),
rewriteable.pop().rehash()
print "done..."
print "Rewriting refs..."
for ref in os.popen('git-for-each-ref'):
hash, type, name = ref.split()
if type != 'commit': continue
if remap.has_key(hash):
hash = remap[hash]
# write updated refs to .git/newrefs
git_update_ref('new' + name, hash)
print "done..."
-
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