Re: [PATCH/RFC v4 02/13] read-cache.c: Re-read index if index file changed

> Add the possibility of re-reading the index file, if it changed
> while reading.
> 
> The index file might change during the read, causing outdated
> information to be displayed. We check if the index file changed
> by using its stat data as heuristic.
> 
> Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
> ---
>  read-cache.c | 87 +++++++++++++++++++++++++++++++++++++++++-------------------
>  1 file changed, 60 insertions(+), 27 deletions(-)
> 
> diff --git a/read-cache.c b/read-cache.c
> index 6a8b4b1..cdd8480 100644
> --- a/read-cache.c
> +++ b/read-cache.c

> @@ -1186,38 +1209,48 @@ int read_index_from(struct index_state *istate, const char *path)
>  	errno = ENOENT;
>  	istate->timestamp.sec = 0;
>  	istate->timestamp.nsec = 0;
> -	fd = open(path, O_RDONLY);
> -	if (fd < 0) {
> -		if (errno == ENOENT)
> -			return 0;
> -		die_errno("index file open failed");
> -	}
> +	do {
> +		err = 0;
> +		fd = open(path, O_RDONLY);
> +		if (fd < 0) {
> +			if (errno == ENOENT)
> +				return 0;
> +			die_errno("index file open failed");
> +		}
>  
> -	if (fstat(fd, &st))
> -		die_errno("cannot stat the open index");
> +		if (fstat(fd, &st_old))
> +			die_errno("cannot stat the open index");
>  
> -	errno = EINVAL;
> -	mmap_size = xsize_t(st.st_size);
> -	mmap = xmmap(NULL, mmap_size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
> -	close(fd);
> -	if (mmap == MAP_FAILED)
> -		die_errno("unable to map index file");
> +		errno = EINVAL;
> +		mmap_size = xsize_t(st_old.st_size);
> +		mmap = xmmap(NULL, mmap_size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
> +		close(fd);
> +		if (mmap == MAP_FAILED)
> +			die_errno("unable to map index file");
>  
> -	hdr = mmap;
> -	if (verify_hdr_version(istate, hdr, mmap_size) < 0)
> -		goto unmap;
> +		hdr = mmap;
> +		if (verify_hdr_version(istate, hdr, mmap_size) < 0)
> +			err = 1;
>  
> -	if (istate->ops->verify_hdr(mmap, mmap_size) < 0)
> -		goto unmap;
> +		if (istate->ops->verify_hdr(mmap, mmap_size) < 0)
> +			err = 1;
>  
> -	istate->ops->read_index(istate, mmap, mmap_size);
> -	istate->timestamp.sec = st.st_mtime;
> -	istate->timestamp.nsec = ST_MTIME_NSEC(st);
> +		if (istate->ops->read_index(istate, mmap, mmap_size) < 0)
> +			err = 1;
> +		istate->timestamp.sec = st_old.st_mtime;
> +		istate->timestamp.nsec = ST_MTIME_NSEC(st_old);
> +		if (lstat(path, &st_new))
> +			die_errno("cannot stat the open index");
>  
> -	munmap(mmap, mmap_size);
> -	return istate->cache_nr;
> +		munmap(mmap, mmap_size);
> +
> +		if (!index_changed(st_old, st_new) && !err)
> +			return istate->cache_nr;
> +
> +		usleep(10*1000);