From 7422bac441d6e00cfb8302600ae64512837ab4e3 Mon Sep 17 00:00:00 2001 From: "Shawn O. Pearce" Date: Sun, 20 Jan 2008 23:37:01 -0500 Subject: [PATCH] Document the hairy gfi_unpack_entry part of fast-import Junio pointed out this part of fast-import wasn't very clear on initial read, and it took some time for someone who was new to fast-import's "dirty little tricks" to understand how this was even working. So a little bit of commentary in the proper place may help future readers. Signed-off-by: Shawn O. Pearce Signed-off-by: Junio C Hamano --- fast-import.c | 33 +++++++++++++++++++++++++++++++++ 1 file changed, 33 insertions(+) diff --git a/fast-import.c b/fast-import.c index f6872fe23d..a523b171e2 100644 --- a/fast-import.c +++ b/fast-import.c @@ -1125,6 +1125,24 @@ static int store_object( return 0; } +/* All calls must be guarded by find_object() or find_mark() to + * ensure the 'struct object_entry' passed was written by this + * process instance. We unpack the entry by the offset, avoiding + * the need for the corresponding .idx file. This unpacking rule + * works because we only use OBJ_REF_DELTA within the packfiles + * created by fast-import. + * + * oe must not be NULL. Such an oe usually comes from giving + * an unknown SHA-1 to find_object() or an undefined mark to + * find_mark(). Callers must test for this condition and use + * the standard read_sha1_file() when it happens. + * + * oe->pack_id must not be MAX_PACK_ID. Such an oe is usually from + * find_mark(), where the mark was reloaded from an existing marks + * file and is referencing an object that this fast-import process + * instance did not write out to a packfile. Callers must test for + * this condition and use read_sha1_file() instead. + */ static void *gfi_unpack_entry( struct object_entry *oe, unsigned long *sizep) @@ -1132,7 +1150,22 @@ static void *gfi_unpack_entry( enum object_type type; struct packed_git *p = all_packs[oe->pack_id]; if (p == pack_data && p->pack_size < (pack_size + 20)) { + /* The object is stored in the packfile we are writing to + * and we have modified it since the last time we scanned + * back to read a previously written object. If an old + * window covered [p->pack_size, p->pack_size + 20) its + * data is stale and is not valid. Closing all windows + * and updating the packfile length ensures we can read + * the newly written data. + */ close_pack_windows(p); + + /* We have to offer 20 bytes additional on the end of + * the packfile as the core unpacker code assumes the + * footer is present at the file end and must promise + * at least 20 bytes within any window it maps. But + * we don't actually create the footer here. + */ p->pack_size = pack_size + 20; } return unpack_entry(p, oe->offset, &type, sizep); -- 2.47.1