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Re: How to feel the real time feature of XFS from userspace

To: harryxiyou <harryxiyou@xxxxxxxxx>
Subject: Re: How to feel the real time feature of XFS from userspace
From: Jeff Liu <jeff.liu@xxxxxxxxxx>
Date: Sat, 09 Nov 2013 15:59:37 +0800
Cc: xfs@xxxxxxxxxxx, zwu.kernel@xxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <CAD+1EGPf=ddMP4vdDxkkWnJH2q9fCSa5uTT-eRAxYLAEtPrLwg@xxxxxxxxxxxxxx>
References: <CAD+1EGPf=ddMP4vdDxkkWnJH2q9fCSa5uTT-eRAxYLAEtPrLwg@xxxxxxxxxxxxxx>
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:11.0) Gecko/20120410 Thunderbird/11.0.1
On 11/09/2013 01:23 PM, harryxiyou wrote:

> Hi all,
> 
> I have format block device with XFS as follows.
> 
> root@node2:~# mkfs.xfs -f -r rtdev=/dev/sda3 /dev/sda4
> 
> meta-data=/dev/sda4              isize=256    agcount=4, agsize=56122440 blks
> 
>          =                       sectsz=512   attr=2, projid32bit=0
> 
> data     =                       bsize=4096   blocks=224489757, imaxpct=25
> 
>          =                       sunit=0      swidth=0 blks
> 
> naming   =version 2              bsize=4096   ascii-ci=0
> 
> log      =internal log           bsize=4096   blocks=109614, version=2
> 
>          =                       sectsz=512   sunit=0 blks, lazy-count=1
> 
> realtime =/dev/sda3              extsz=4096   blocks=14865657,
> rtextents=14865657
> 
> 
> And I also write user-space codes as follows.
> 
> root@node2:~/test# cat xfs.c
> #include <stdio.h>
> #include <unistd.h>
> #include <sys/types.h>
> #include <sys/stat.h>
> #include <fcntl.h>
> #include <xfs/xfs.h>
> #include <xfs/xfs_fs.h>
> 
> int main(int argc, char **argv) {
> int fd;
> int xfs_ret = 0;
> 
> fd = open("./1", O_RDWR);
> if (fd < 0) {
> fprintf(stderr, "open error!\n");
> return -1;
> }
> xfs_ret = xfsctl("./1", fd, XFS_IOC_FSGETXATTR, NULL);
> 
> return 0;
> }
> 
> 
> Now, I am wondering how to feel the real time feature of XFS from userspace?
> Could anyone please give me some suggestions? Thanks in advance.

Mount your realtime device at first:
mount -o rtdev=/dev/sda3 /dev/sda4 /mount_point

Then you need to mark the attribute bit set with XFS_XFLAG_REALTIME via 
xfsctl(3)
after file creation before writing any data to the file, hence your demo code
would looks like:

struct fsxattr  attr;

attr.fsx_xflags |= XFS_XFLAG_REALTIME;
xfs_ret = xfsctl(target_file_path, fd, XFS_IOC_FSSETXATTR, &attr);
...

I would suggest you take a look at the source of xfs_rctp(8) at xfsprogs to get
more info.

BTW, I remember Dave once mentioned that the realtime feature on Linux is not 
widely
tested and not recommended for production use.


Thanks,
-Jeff

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