Subject: Re: [PATCH] fix recursive-merge of empty files with different permissions

From: Junio C Hamano <[email-masked]>
Date: Thu, 13 Mar 2008 11:50:08 -0700

Johannes Schindelin <[email-masked]> writes:

> diff --git a/builtin-merge-file.c b/builtin-merge-file.c
> index adce6d4..cde4b2c 100644
> --- a/builtin-merge-file.c
> +++ b/builtin-merge-file.c
> @@ -57,7 +57,8 @@ int cmd_merge_file(int argc, const char **argv, const char *prefix)
>  
>  		if (!f)
>  			ret = error("Could not open %s for writing", filename);
> -		else if (fwrite(result.ptr, result.size, 1, f) != 1)
> +		else if (result.size &&
> +				fwrite(result.ptr, result.size, 1, f) != 1)
>  			ret = error("Could not write to %s", filename);
>  		else if (fclose(f))
>  			ret = error("Could not close %s", filename);

Lol.  We are dealing with N-byte quantity so we send one record of length
N and make sure we processed one record, and it does not work when N is
zero.

We could instead send N records of size 1 and make sure we processed N
records to lose the conditional instead, but the patch avoids unnecessary
call to fread/fwrite so that is good.  Thanks.

It felt funny because my current bedtime reading happens to be "Zero: The
Biography of a Dangerous Idea (ISBN 0140296476)".

> diff --git a/xdiff-interface.c b/xdiff-interface.c
> index bba2364..61dc5c5 100644
> --- a/xdiff-interface.c
> +++ b/xdiff-interface.c
> @@ -152,8 +152,8 @@ int read_mmfile(mmfile_t *ptr, const char *filename)
>  	if ((f = fopen(filename, "rb")) == NULL)
>  		return error("Could not open %s", filename);
>  	sz = xsize_t(st.st_size);
> -	ptr->ptr = xmalloc(sz);
> -	if (fread(ptr->ptr, sz, 1, f) != 1)
> +	ptr->ptr = xmalloc(sz ? sz : 1);
> +	if (sz && fread(ptr->ptr, sz, 1, f) != 1)
>  		return error("Could not read %s", filename);
>  	fclose(f);
>  	ptr->size = sz;

Do you need to actually allocate ptr->ptr when sz is zero, instead of
setting it to NULL, like:

	sz = xsize_t(st.st_size);
	ptr->size = sz;
        if (!sz)
        	ptr->ptr = NULL;
	else {
        	ptr->ptr = xmalloc(sz);
		if (fread(ptr->ptr, 1, sz, f) != sz)
			return error("Could not read %s", filename);
	}
	fclose(f);