Nguyễn Thái Ngọc Duy writes:
> If an entry is "watched", git lets an external program decide if the
> entry is modified or not. It's more like --assume-unchanged, but
> designed to be controlled by machine.
>
> We are running out of on-disk ce_flags, so instead of extending
> on-disk entry format again, "watched" flags are in-core only and
> stored as extension instead.
As you said yourself in
http://thread.gmane.org/gmane.comp.version-control.git/240339/focus=240385
this is not quite true. As for your explanation there,
> Anyway using extended flags means 2 extra bytes per entry for
> almost every entry in this case (and for index v5 it means redoing
> crc32 for almost every entry too when the bit is updated) so it may
> still be a good idea to keep the new flag separate.
I don't think adding 2 extra bytes would be too bad, since we are
already using 62 bytes plus the bytes for the filename for each index
entry, so it would be a less than 3% increase in the index file size.
(And the extended flags may be used anyway in some cases)
As for index-v5 (if that's ever going to happen), it depends mostly on
how often the CE_WATCHED is going to be updated, to decide whether it
makes sense to store this as extension.
That said, I don't care too deeply if it's stored one way or another,
but I think it would be good to update the commit message with a better
rationale for the choice.
> Signed-off-by: Nguyễn Thái Ngọc Duy
> ---
> cache.h | 2 ++
> read-cache.c | 41 -
> 2 files changed, 42 insertions(+), 1 deletion(-)
>
> diff --git a/cache.h b/cache.h
> index a09d622..069dce7 100644
> --- a/cache.h
> +++ b/cache.h
> @@ -168,6 +168,8 @@ struct cache_entry {
> /* used to temporarily mark paths matched by pathspecs */
> #define CE_MATCHED (1 << 26)
>
> +#define CE_WATCHED (1 << 27)
> +
> /*
> * Extended on-disk flags
> */
> diff --git a/read-cache.c b/read-cache.c
> index fe1d153..6f21e3f 100644
> --- a/read-cache.c
> +++ b/read-cache.c
> @@ -33,6 +33,7 @@ static struct cache_entry *refresh_cache_entry(struct
> cache_entry *ce, int reall
> #define CACHE_EXT(s) ( (s[0]<<24)|(s[1]<<16)|(s[2]<<8)|(s[3]) )
> #define CACHE_EXT_TREE 0x54524545/* "TREE" */
> #define CACHE_EXT_RESOLVE_UNDO 0x52455543 /* "REUC" */
> +#define CACHE_EXT_WATCH 0x57415443 /* "WATC" */
>
> struct index_state the_index;
>
> @@ -1293,6 +1294,19 @@ static int verify_hdr(struct cache_header *hdr,
> return 0;
> }
>
> +static void read_watch_extension(struct index_state *istate, uint8_t *data,
> + unsigned long sz)
> +{
> + int i;
> + if ((istate->cache_nr + 7) / 8 != sz) {
> + error("invalid 'WATC' extension");
> + return;
> + }
> + for (i = 0; i < istate->cache_nr; i++)
> + if (data[i / 8] & (1 << (i % 8)))
> + istate->cache[i]->ce_flags |= CE_WATCHED;
> +}
> +
> static int read_index_extension(struct index_state *istate,
> const char *ext, void *data, unsigned long sz)
> {
> @@ -1303,6 +1317,9 @@ static int read_index_extension(struct index_state
> *istate,
> case CACHE_EXT_RESOLVE_UNDO:
> istate->resolve_undo = resolve_undo_read(data, sz);
> break;
> + case CACHE_EXT_WATCH:
> + read_watch_extension(istate, data, sz);
> + break;
> default:
> if (*ext < 'A' || 'Z' < *ext)
> return error("index uses %.4s extension, which we do
> not understand",
> @@ -1781,7 +1798,7 @@ int write_index(struct index_state *istate, int newfd)
> {
> git_SHA_CTX c;
> struct cache_header hdr;
> - int i, err, removed, extended, hdr_version;
> + int i, err, removed, extended, hdr_version, has_watches = 0;
> struct cache_entry **cache = istate->cache;
> int entries = istate->cache_nr;
> struct stat st;
> @@ -1790,6 +1807,8 @@ int write_index(struct index_state *istate, int newfd)
> for (i = removed = extended = 0; i < entries; i++) {
> if (cache[i]->ce_flags & CE_REMOVE)
> removed++;
> + else if (cache[i]->ce_flags & CE_WATCHED)
> + has_watches++;
>
> /* reduce extended entries if possible */
> cache[i]->ce_flags &= ~CE_EXTENDED;
> @@ -1861,6 +1880,26 @@ int write_index(struct index_state *istate, int newfd)
> if (err)
> return -1;
> }
> + if (has_watches) {
> + int id, sz = (entries - removed + 7) / 8;
> + uint8_t *data = xmalloc(sz);
> + memset(data, 0, sz);
> + for (i = 0, id = 0; i < entries && has_watches; i++) {
> + struct cache_entry *ce = cache[i];
> + if (ce->ce_flags & CE_REMOVE)
> + continue;
> + if (ce->ce_flags &
