linux-kernel - Re: [PATCH v2 10/13] perf header: add a buffer to struct feat

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Date:   Thu, 25 May 2017 10:08:48 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     David Carrillo-Cisneros <davidcc@...gle.com>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>, Simon Que <sque@...omium.org>,
        Wang Nan <wangnan0@...wei.com>, Jiri Olsa <jolsa@...nel.org>,
        He Kuang <hekuang@...wei.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        David Ahern <dsa@...ulusnetworks.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Stephane Eranian <eranian@...gle.com>,
        Paul Turner <pjt@...gle.com>
Subject: Re: [PATCH v2 10/13] perf header: add a buffer to struct feat_fd

On Tue, May 23, 2017 at 12:48:50AM -0700, David Carrillo-Cisneros wrote:

SNIP

> @@ -82,11 +83,27 @@ bool perf_header__has_feat(const struct perf_header *header, int feat)
>  /* Return: 0 if succeded, -ERR if failed. */
>  int do_write(struct feat_fd *fd, const void *buf, size_t size)
>  {
> -	ssize_t ret;
> +	void *addr;
>  
> -	ret  = writen(fd->fd, buf, size);
> -	if (ret != (ssize_t)size)
> -		return ret < 0 ? (int)ret: -1;
> +	if (!fd->buf) {
> +		ssize_t ret = writen(fd->fd, buf, size);
> +
> +		if (ret != (ssize_t)size)
> +			return ret < 0 ? (int)ret : -1;
> +		return 0;
> +	}
> +retry:
> +	if (size > (fd->size - fd->offset)) {
> +		addr = realloc(fd->buf, fd->size << 1);
> +		if (!addr)
> +			return -ENOSPC;
> +		fd->buf = addr;
> +		fd->size <<= 1;
> +		goto retry;
> +	}
> +
> +	memcpy(fd->buf + fd->offset, buf, size);
> +	fd->offset += size;
>  
>  	return 0;

please put those 2 cases in separate functions

>  }
> @@ -126,10 +143,21 @@ static int do_write_string(struct feat_fd *fd, const char *str)
>  
>  static int __do_read(struct feat_fd *fd, void *addr, ssize_t size)
>  {
> -	ssize_t ret = readn(fd->fd, addr, size);
> +	if (!fd->buf) {
> +		ssize_t ret = readn(fd->fd, addr, size);
> +
> +		if (ret != (ssize_t)size)
> +			return ret < 0 ? (int)ret : -1;
> +		return 0;
> +	}
> +
> +	assert((ssize_t)fd->size > fd->offset);
> +	if (size > (ssize_t)fd->size - fd->offset)
> +		return -1;
> +
> +	memcpy(addr, fd->buf + fd->offset, size);
> +	fd->offset += size;
>  
> -	if (ret != (ssize_t)size)
> -		return ret < 0 ? (int)ret : -1;
>  	return 0;
>  }

same for the read

thanks,
jirka