Subject: Re: [GSoC PATCH v2 2/4] pack-write: add helper to fill promisor file after repack

From: Lorenzo Pegorari <[email-masked]>
Date: Thu, 26 Mar 2026 17:15:02 +0100

On Mon, Mar 23, 2026 at 04:27:44PM -0400, Eric Sunshine wrote:
> On Sun, Mar 22, 2026 at 3:18 PM LorenzoPegorari
> <[email-masked]> wrote:
> > Create a `copy_all_promisor_files()` helper function used to copy the
> > contents of all ".promisor" files in a `repository` inside another
> > ".promisor" file.
> >
> > This function can be used to preserve the contents of all ".promisor"
> > files inside a new ".promisor" file, for example when a repack happens.
> >
> > This function is written in such a way so that it will read all the
> > ".promisor" files inside the given `repository` line by line, and copy
> > only the lines that are not already present in the destination file. This
> > is done to avoid copying the same lines multiple times that may come from
> > multiple (redundant) packfiles. There might be another better/cleaner way
> > to achieve this.
> >
> > Signed-off-by: LorenzoPegorari <[email-masked]>
> > ---
> 
> Thanks, I think this version addresses all my review comments[*] and
> looks much better overall. Use of `strset` makes a big difference over
> the previous attempt. A couple minor comments below...
> 
> [*]: https://lore.kernel.org/git/CAPig+cQSsMfvHJnwuXGQ1Je8ekz=[email-masked]/
> 
> > diff --git a/pack-write.c b/pack-write.c
> > @@ -621,3 +622,63 @@ void write_promisor_file(const char *promisor_name, struct ref **sought, int nr_
> > +void copy_all_promisor_files(struct repository *repo, const char *promisor_name)
> > +{
> > +       struct strset dest_content = STRSET_INIT;
> > +       struct strbuf read_line = STRBUF_INIT;
> > +       struct strbuf promisor_source_name = STRBUF_INIT;
> > +       struct strbuf write_dest = STRBUF_INIT;
> > +       FILE *dest, *source;
> > +       struct packed_git *p;
> > +       int err;
> 
> Nit: I probably would have declared `FILE *dest` within the scope of
> the repo_for_each_pack() loop as suggested in the review, but it's not
> worth a reroll.

Ack. I will fix it. Thanks!

> > +       dest = xfopen(promisor_name, "r+");
> > +       while (strbuf_getline(&read_line, dest) != EOF)
> > +               strset_add(&dest_content, read_line.buf);
> > +
> > +       repo_for_each_pack(repo, p) {
> > +               if (!p->pack_promisor)
> > +                       continue;
> > +
> > +               strbuf_reset(&promisor_source_name);
> > +               strbuf_addstr(&promisor_source_name, p->pack_name);
> > +               strbuf_strip_suffix(&promisor_source_name, ".pack");
> > +               strbuf_addstr(&promisor_source_name, ".promisor");
> > +               source = xfopen(promisor_source_name.buf, "r");
> > +
> > +               /*
> > +                * For each line of the promisor source file, check if it already
> > +                * is in the promisor dest file. If not, add it to write_dest, so
> > +                * that it will be written in the dest file.
> > +                */
> > +               while (strbuf_getline(&read_line, source) != EOF) {
> > +                       if (strset_add(&dest_content, read_line.buf)) {
> > +                               strbuf_addbuf(&write_dest, &read_line);
> > +                               strbuf_addstr(&write_dest, "\n");
> 
> Not worth a reroll, but this could also be:
> 
>     strbuf_addch(&write_dest, '\n');

Ack.

> > +                       }
> > +               }
> > +
> > +               err = ferror(source);
> > +               err |= fclose(source);
> > +               if (err)
> > +                       die(_("could not read '%s' promisor file"), promisor_source_name.buf);
> > +       }
> > +
> > +       if (write_dest.len) {
> > +               strbuf_strip_suffix(&write_dest, "\n");
> > +               if (fseek(dest, 0L, SEEK_END))
> > +                       die_errno(_("fseek failed"));
> > +               fprintf(dest, "%s\n", write_dest.buf);
> > +       }
> 
> Can you explain why you strip "\n" and then re-add it via fprintf()?
> The reason is not immediately obvious.

Stripping it and then adding it again is actually not necessary. I think
it was necessary in a previous iteration. Thanks for noticing, will fix!

> > +       err = ferror(dest);
> > +       err |= fclose(dest);
> > +       if (err)
> > +               die(_("could not write '%s' promisor file"), promisor_name);
> > +
> > +       strbuf_release(&read_line);
> > +       strbuf_release(&promisor_source_name);
> > +       strbuf_release(&write_dest);
> > +       strset_clear(&dest_content);
> > +}
> 
> Everything appears to be released. Good.

Thank you so much for your help Eric,

Lorenzo