linux-kernel - Re: [PATCH] initramfs: clean old path before creating a hardlink

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Date:   Thu, 22 Nov 2018 09:55:22 +0800
From:   Li Zhijian <lizhijian@...fujitsu.com>
To:     <linux-kernel@...r.kernel.org>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Andrew Morton <akpm@...ux-foundation.org>
CC:     <zhijianx.li@...el.com>, Philip Li <philip.li@...el.com>
Subject: Re: [PATCH] initramfs: clean old path before creating a hardlink

ping

This patch is to fix initrd cannot be extracted properly in some cases.


Thanks


On 11/16/2018 03:12 PM, Li Zhijian wrote:
> Previously, sys_link() will fail due to the new path is already existed.
> this case ofen appears when we use a concated initrd, below is an
> sample:
>
> 1) prepare a basic rootfs, it contains a regular files rc.local
> lizhijian@:~/yocto-tiny-i386-2016-04-22$ cat etc/rc.local
>   #!/bin/sh
>   echo "Running /etc/rc.local..."
> yocto-tiny-i386-2016-04-22$ find . | sed 's,^\./,,' | cpio -o -H newc | gzip -n -9 >../rootfs.cgz
>
> 2) create a extra initrd which also includes a etc/rc.local
> lizhijian@:~/lkp-x86_64/etc$ echo "append initrd" >rc.local
> lizhijian@:~/lkp/lkp-x86_64/etc$ cat rc.local
> append initrd
> lizhijian@:~/lkp/lkp-x86_64/etc$ ln rc.local rc.local.hardlink
> append initrd
> lizhijian@:~/lkp/lkp-x86_64/etc$ stat rc.local rc.local.hardlink
>    File: 'rc.local'
>    Size: 14        	Blocks: 8          IO Block: 4096   regular file
> Device: 801h/2049d	Inode: 11296086    Links: 2
> Access: (0664/-rw-rw-r--)  Uid: ( 1002/lizhijian)   Gid: ( 1002/lizhijian)
> Access: 2018-11-15 16:08:28.654464815 +0800
> Modify: 2018-11-15 16:07:57.514903210 +0800
> Change: 2018-11-15 16:08:24.180228872 +0800
>   Birth: -
>    File: 'rc.local.hardlink'
>    Size: 14        	Blocks: 8          IO Block: 4096   regular file
> Device: 801h/2049d	Inode: 11296086    Links: 2
> Access: (0664/-rw-rw-r--)  Uid: ( 1002/lizhijian)   Gid: ( 1002/lizhijian)
> Access: 2018-11-15 16:08:28.654464815 +0800
> Modify: 2018-11-15 16:07:57.514903210 +0800
> Change: 2018-11-15 16:08:24.180228872 +0800
>   Birth: -
>
> lizhijian@:~/lkp/lkp-x86_64$ find . | sed 's,^\./,,' | cpio -o -H newc | gzip -n -9 >../rc-local.cgz
> lizhijian@:~/lkp/lkp-x86_64$ gzip -dc ../rc-local.cgz | cpio -t
> .
> etc
> etc/rc.local.hardlink <<< it will be extracted first at this initrd
> etc/rc.local
>
> 3) concate 2 initrds and boot
> lizhijian@:~/lkp$ cat rootfs.cgz rc-local.cgz >concate-initrd.cgz
> lizhijian@:~/lkp$ qemu-system-x86_64 -nographic -enable-kvm -cpu host -smp 1 -m 1024 -kernel ~/lkp/linux/arch/x86/boot/bzImage -append "console=ttyS0 earlyprint=ttyS0 ignore_loglevel" -initrd ./concate-initr.cgz -serial stdio -nodefaults
>
> In this case, sys_link(2) will fail and return -EEXIST, so we can only
> get the rc.local at rootfs.cgz instead of rc-local.cgz
>
> CC: Philip Li <philip.li@...el.com>
> Signed-off-by: Li Zhijian <lizhijian@...fujitsu.com>
> ---
>   init/initramfs.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/init/initramfs.c b/init/initramfs.c
> index 6405577..381fd4c 100644
> --- a/init/initramfs.c
> +++ b/init/initramfs.c
> @@ -291,12 +291,16 @@ static int __init do_reset(void)
>   	return 1;
>   }
>   
> +static void __init clean_path(char *path, umode_t fmode);
> +
>   static int __init maybe_link(void)
>   {
>   	if (nlink >= 2) {
>   		char *old = find_link(major, minor, ino, mode, collected);
> -		if (old)
> +		if (old) {
> +			clean_path(collected, 0);
>   			return (ksys_link(old, collected) < 0) ? -1 : 1;
> +		}
>   	}
>   	return 0;
>   }