René Scharfe <l.s.r@xxxxxx> writes:
> How about the patch below? Before it checks if an index entry exists
> in the work tree, it checks if its path includes a symlink.
Honestly, I didn't expect the fix to be in the refresh-index code
path, but doing this there sort of makes sense.
I think you, who dug to find out where to add the check, already
know this, and I am writing this mainly for myself and for the list
archive, but when the knee-jerk "has-syjmlink-leading-path missing?"
reaction came to me, two obvious optimizations also came to my mind:
- When checking a cache entry "a/b/c/d/e" and we find out "a/b/c"
is a symbolic link, we mark it as ~CE_VALID, but at the same
time, we learn "a/b/c/any/thing" are also ~CE_VALID with that
check, so we _could_, after the has_symlink_leading_path once
returns true, so there may be an opportunity to fast-forward the
scan, marking all paths under "a/b/c" as ~CE_VALID.
- After finding out "a/b/c" is a symbolic link to cause anything
underneath marked as ~CE_VALID, we also know "a/" and "a/b/"
exists as real directories, so a later check for "a/b/some/thing"
can start checking at "a/b/some/" without checking "a/" and "a/b/".
The latter is more important as it is a much more common case that
the shape of the working tree not to change.
But I think the implementation of has_symlink_leading_path() already
has these optimizations built inside around the (unfortunately named)
"struct cache_def", so it probably would not give us much boost to
implement such a fast-forwarding of the scan.
> And do we need to use the threaded_ variant of the function here?
Hmmm, this is a tangent, but you comment made me wonder if we also
need to adjust preload_thread() in preload-index.c somehow, but we
do not touch CE_UPTODATE there, so it probably is not necessary.
The caller of refresh_cache_ent() is walking an array of sorted
pathnames aka istate->cache[] in a single-threaded fashion, possibly
with a pathspec to limit the scan. Do you mean that we may want to
make istate->cache[] scanned by multiple threads? I am not sure.
> diff --git a/read-cache.c b/read-cache.c
> index 5d3c8bd..6f0057f 100644
> --- a/read-cache.c
> +++ b/read-cache.c
> @@ -1064,6 +1064,14 @@ static struct cache_entry *refresh_cache_ent(struct index_state *istate,
> return ce;
> }
>
> + if (has_symlink_leading_path(ce->name, ce_namelen(ce))) {
> + if (ignore_missing)
> + return ce;
> + if (err)
> + *err = ENOENT;
> + return NULL;
> + }
> +
> if (lstat(ce->name, &st) < 0) {
> if (ignore_missing && errno == ENOENT)
> return ce;
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