linux-kernel - Re: [RFC v11][PATCH 03/13] General infrastructure for checkpoint restart

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Message-ID: <4947FBC8.2000601@google.com>
Date:	Tue, 16 Dec 2008 11:04:40 -0800
From:	Mike Waychison <mikew@...gle.com>
To:	Oren Laadan <orenl@...columbia.edu>
CC:	jeremy@...p.org, arnd@...db.de, linux-api@...r.kernel.org,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org,
	Dave Hansen <dave@...ux.vnet.ibm.com>, linux-mm@...ck.org,
	Linux Torvalds <torvalds@...l.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC v11][PATCH 03/13] General infrastructure for checkpoint
 restart

Oren Laadan wrote:

> +/*
> + * Helpers to write(read) from(to) kernel space to(from) the checkpoint
> + * image file descriptor (similar to how a core-dump is performed).
> + *
> + *   cr_kwrite() - write a kernel-space buffer to the checkpoint image
> + *   cr_kread() - read from the checkpoint image to a kernel-space buffer
> + */
> +
> +int cr_kwrite(struct cr_ctx *ctx, void *addr, int count)
> +{
> +	struct file *file = ctx->file;
> +	mm_segment_t fs;
> +	ssize_t nwrite;
> +	int nleft;
> +
> +	fs = get_fs();
> +	set_fs(KERNEL_DS);
> +	for (nleft = count; nleft; nleft -= nwrite) {
> +		nwrite = file->f_op->write(file, addr, nleft, &file->f_pos);
> +		if (nwrite < 0) {
> +			if (nwrite == -EAGAIN)
> +				nwrite = 0;
> +			else

set_fs(fs) here

> +				return nwrite;
> +		}
> +		addr += nwrite;
> +	}
> +	set_fs(fs);
> +	ctx->total += count;
> +	return 0;
> +}
> +
> +int cr_kread(struct cr_ctx *ctx, void *addr, int count)
> +{
> +	struct file *file = ctx->file;
> +	mm_segment_t fs;
> +	ssize_t nread;
> +	int nleft;
> +
> +	fs = get_fs();
> +	set_fs(KERNEL_DS);
> +	for (nleft = count; nleft; nleft -= nread) {
> +		nread = file->f_op->read(file, addr, nleft, &file->f_pos);
> +		if (nread <= 0) {
> +			if (nread == -EAGAIN) {
> +				nread = 0;
> +				continue;
> +			} else if (nread == 0)
> +				nread = -EPIPE;		/* unexecpted EOF */

set_fs(fs) here as well

> +			return nread;
> +		}
> +		addr += nread;
> +	}
> +	set_fs(fs);
> +	ctx->total += count;
> +	return 0;
> +}
> +

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