linux-kernel - Re: [RFC 4/4] nbd: Add support for nbd as root device

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Message-ID: <20150120115105.GA26529@pengutronix.de>
Date:	Tue, 20 Jan 2015 12:51:05 +0100
From:	Markus Pargmann <mpa@...gutronix.de>
To:	Paul Clements <Paul.Clements@...eleye.com>
Cc:	nbd-general@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	kernel@...gutronix.de
Subject: Re: [RFC 4/4] nbd: Add support for nbd as root device

On Tue, Jan 13, 2015 at 02:44:25PM +0100, Markus Pargmann wrote:
> Adding support to nbd to use it as a root device. This code essentially
> provides a minimal nbd-client implementation within the kernel. It opens
> a socket and makes the negotiation with the server. Afterwards it passes
> the socket to the normal nbd-code to handle the connection.
> 
> The arguments for the server are passed via module parameter. The
> module parameter has the format
> '[<SERVER_IP>:]<SERVER_PORT>/<EXPORT_NAME>'.
> SERVER_IP is optional. If it is not available it will use the
> root_server_addr transmitted through DHCP.
> 
> Based on those arguments, the connection to the server is established
> and is connected to the nbd0 device. The rootdevice therefore is
> root=/dev/nbd0.
> 
> Signed-off-by: Markus Pargmann <mpa@...gutronix.de>
> ---
>  drivers/block/nbd.c | 306 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 306 insertions(+)
> 
> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index 11f7644be111..ac881ae3c15a 100644
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -32,12 +32,17 @@
>  #include <net/sock.h>
>  #include <linux/net.h>
>  #include <linux/kthread.h>
> +#include <net/ipconfig.h>
> +#include <linux/in.h>
> +#include <linux/tcp.h>
>  
>  #include <asm/uaccess.h>
>  #include <asm/types.h>
>  
>  #include <linux/nbd.h>
>  
> +#define ADDR_NONE cpu_to_be32(INADDR_NONE)
> +
>  #define NBD_MAGIC 0x68797548
>  
>  #ifdef NDEBUG
> @@ -71,6 +76,20 @@ static int max_part;
>   */
>  static DEFINE_SPINLOCK(nbd_lock);
>  
> +static const char nbd_magic[] = "NBDMAGIC";
> +static const u64 nbd_opts_magic = 0x49484156454F5054LL;
> +
> +/* Options used for the kernel driver */
> +#define NBD_OPT_EXPORT_NAME 1
> +
> +#define NBD_DEFAULT_BLOCKSIZE 1024
> +
> +extern __be32 root_nfs_parse_addr(char *name);
> +
> +static __be32 nbd_server_addr = ADDR_NONE;
> +static __be32 nbd_server_port;
> +static char nbd_server_export[128] = "";
> +
>  #ifndef NDEBUG
>  static const char *ioctl_cmd_to_ascii(int cmd)
>  {
> @@ -105,6 +124,52 @@ static const char *nbdcmd_to_ascii(int cmd)
>  }
>  #endif /* NDEBUG */
>  
> +/*
> + * Parse format "[<SERVER_IP>:]<SERVER_PORT>/<EXPORT_NAME>"
> + */
> +static int nbd_server_addr_set(const char *val, const struct kernel_param *kp)
> +{
> +	char *export;
> +	u16 port;
> +	int ret;
> +	char buf[128];
> +
> +	strncpy(buf, val, 128);
> +
> +	nbd_server_addr = root_nfs_parse_addr(buf);
> +
> +	if (*buf == '\0') {
> +		ret = -EINVAL;
> +		goto free_buf;
> +	}
> +	export = strchr(buf, '/');
> +	if (!export || *(export + 1) == '\0') {
> +		ret = -EINVAL;
> +		goto free_buf;
> +	}
> +	*export = '\0';
> +	++export;
> +
> +	ret = kstrtou16(buf, 10, &port);
> +	if (ret)
> +		goto free_buf;
> +
> +	memmove(buf, export, strlen(export) + 1);

This memmove() is a leftover from a previous version, it is removed for
the next series version. I also added some documentation patches that
describe this feature in Documentation/blockdev/nbd.txt. I will send it
at the end of this week.

Best regards,

Markus

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