Re: [PATCH v2 4/4] fsmonitor: Delay updating state until after split index is merged

> If the fsmonitor extension is used in conjunction with the split index
> extension, the set of entries in the index when it is first loaded is
> only a subset of the real index.  This leads to only the non-"base"
> index being marked as CE_FSMONITOR_VALID.
> 
> Delay the expansion of the ewah bitmap until after tweak_split_index
> has been called to merge in the base index as well.
> 
> The new fsmonitor_dirty is kept from being leaked by dint of being
> cleaned up in post_read_index_from, which is guaranteed to be called
> after do_read_index in read_index_from.
> 
> Signed-off-by: Alex Vandiver <alexmv@dropbox.com>
> ---
>   cache.h     |  1 +
>   fsmonitor.c | 39 ++++++++++++++++++++++++---------------
>   2 files changed, 25 insertions(+), 15 deletions(-)
> 
> diff --git a/cache.h b/cache.h
> index 25adcf681..0a4f43ec2 100644
> --- a/cache.h
> +++ b/cache.h
> @@ -348,6 +348,7 @@ struct index_state {
>   	unsigned char sha1[20];
>   	struct untracked_cache *untracked;
>   	uint64_t fsmonitor_last_update;
> +	struct ewah_bitmap *fsmonitor_dirty;
>   };
>   
>   extern struct index_state the_index;
> diff --git a/fsmonitor.c b/fsmonitor.c
> index 0d26ff34f..fad9c6b13 100644
> --- a/fsmonitor.c
> +++ b/fsmonitor.c
> @@ -49,20 +49,7 @@ int read_fsmonitor_extension(struct index_state *istate, const void *data,
>   		ewah_free(fsmonitor_dirty);
>   		return error("failed to parse ewah bitmap reading fsmonitor index extension");
>   	}
> -
> -	if (git_config_get_fsmonitor()) {
> -		/* Mark all entries valid */
> -		for (i = 0; i < istate->cache_nr; i++)
> -			istate->cache[i]->ce_flags |= CE_FSMONITOR_VALID;
> -
> -		/* Mark all previously saved entries as dirty */
> -		ewah_each_bit(fsmonitor_dirty, fsmonitor_ewah_callback, istate);
> -
> -		/* Now mark the untracked cache for fsmonitor usage */
> -		if (istate->untracked)
> -			istate->untracked->use_fsmonitor = 1;
> -	}
> -	ewah_free(fsmonitor_dirty);
> +	istate->fsmonitor_dirty = fsmonitor_dirty;
>   
>   	trace_printf_key(&trace_fsmonitor, "read fsmonitor extension successful");
>   	return 0;
> @@ -239,7 +226,29 @@ void remove_fsmonitor(struct index_state *istate)
>   
>   void tweak_fsmonitor(struct index_state *istate)
>   {
> -	switch (git_config_get_fsmonitor()) {
> +	int i;
> +	int fsmonitor_enabled = git_config_get_fsmonitor();
> +

> +	if (istate->fsmonitor_dirty) {
> +		if (fsmonitor_enabled) {
> +			/* Mark all entries valid */
> +			for (i = 0; i < istate->cache_nr; i++) {
> +				istate->cache[i]->ce_flags |= CE_FSMONITOR_VALID;
> +			}
> +
> +			/* Mark all previously saved entries as dirty */
> +			ewah_each_bit(istate->fsmonitor_dirty, fsmonitor_ewah_callback, istate);
> +
> +			/* Now mark the untracked cache for fsmonitor usage */
> +			if (istate->untracked)
> +				istate->untracked->use_fsmonitor = 1;
> +		}
> +
> +		ewah_free(istate->fsmonitor_dirty);
> +		istate->fsmonitor_dirty = NULL;
> +	}
> +
> +	switch (fsmonitor_enabled) {
>   	case -1: /* keep: do nothing */
>   		break;
>   	case 0: /* false */
>