Re: 4.8.2: device/sysdep_LINUX.c

[Martin Pala]

Hi, sorry for the delay.

I have looked on it, you are right. Although the linux documentation of 
statvfs f_blocks says, that it is in f_frsize units, it seems that in 
fact the f_bsize is used.

I have tested it with different blocks sizes and filesystems (ext3, 
vfat, ntfs, udf) ... in all these cases the f_frsize was equal to 
f_bsize and monit provided correct result.

The NFS is different as you described - it reports 512B f_frsize and 
32KB f_bsize ... the f_blocks here is obviously in f_bsize. The monit 
result based on the f_frsize to f_bsize conversion was invalid.

The device/sysdep_LINUX.c was fixed, thanks for the patch and help :)

Martin


Aaron Scamehorn wrote:
> Hi Martin,
>
> I don't think your assumption about f_bsize == f_frsize is valid.  And
> if it is, what is the point of multiplying by (usage.f_frsize /
> usage.f_bsize), which is always 1?
>
> I don't see anything in the POSIX docs for statvfs stating that this
> math is necessary, nor that f_bsize == f_frsize is a rule.
>
> I didn't see anything in the GNU coreutils package (df, du, stat, etc)
> doing this math either.
>
> One place that this assumption breaks is for an nfs mounted partition;
> The default blocksize is 8K, usually larger (32K).
>
> Please look at the attached test program, and it's associated output.
>
> I think you'll see that statvfs is ultimately making the same system
> call that statfs does (as evidenced by the strace output), which gives
> you the proper f_blocks without any additional math necessary.
>
> Thanks,
> Aaron
>
>
> -----Original Message-----
> From: address@hidden
> [mailto:address@hidden On
> Behalf Of Martin Pala
> Sent: Friday, November 17, 2006 4:28 PM
> To: The monit developer list
> Subject: Re: 4.8.2: device/sysdep_LINUX.c
>
> Hi,
>
> the blocks size is computed according to statvfs structure description
> (see 'man statvfs'):
>
> --8<--
>           struct statvfs {
>             unsigned long  f_bsize;    /* file system block size */
>             unsigned long  f_frsize;   /* fragment size */
>             fsblkcnt_t     f_blocks;   /* size of fs in f_frsize units
> */
>             fsblkcnt_t     f_bfree;    /* # free blocks */
>             fsblkcnt_t     f_bavail;   /* # free blocks for non-root */
>             fsfilcnt_t     f_files;    /* # inodes */
>             fsfilcnt_t     f_ffree;    /* # free inodes */
>             fsfilcnt_t     f_favail;   /* # free inodes for non-root */
>             unsigned long  f_fsid;     /* file system ID */
>             unsigned long  f_flag;     /* mount flags */
>             unsigned long  f_namemax;  /* maximum filename length */
>           };
> --8<--
>
> f_blocks has to be recomputed this way since it describes the number of
> fragments, not blocks (the f_bsize and f_frsize match on all linuxes
> which i ever saw even with different block sizes).
>
> Martin
>
>
> Aaron Scamehorn wrote:
> > Hello,
> >
> > In device_usage_sysdep:
> >
> > I'm not quite sure what the following is supposed to be calculating:
> >
> > inf->f_blocks=          usage.f_blocks * usage.f_frsize /
> usage.f_bsize;
> > I think you're incorrectly mixing block size & fragment sizes.  I 
> > don't think they have anything to do with each other.
> >
> > You're probably just getting lucky, because your f_frsize & f_bsize 
> > both = 4K.
> >
> > However, on large filesystems, where f_bsize might be 32K, you'll get 
> > crazy usage numbers.
> >
> > I think you just want:
> >
> > inf->f_blocks=          usage.f_blocks ;
> >
> >
> > Thanks,
> > Aaron
> >
> >
> > 25        if(statvfs( dir, &usage) != 0) {
> > (gdb) n
> > (gdb) print usage
> > $1 = {f_bsize = 32768, f_frsize = 4096, f_blocks = 8811322, f_bfree = 
> > 8053030, f_bavail = 7605440,
> >   f_files = 35815424, f_ffree = 35800806, f_favail = 35800806, f_fsid 
> > = 0, __f_unused = 0, f_flag = 0,
> >     f_namemax = 255, __f_spare = {0, 0, 0, 0, 0, 0}}
> >
> >
> > _______________________________________________
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>
>
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> ------------------------------------------------------------------------
>
> Script started on Mon 20 Nov 2006 11:39:20 AM CST
> address@hidden ~]$ a.out /cogcap
> -------------Incorrect f_blocks----------
> f_blocks=15073280
> Blocks free for non superuser 1540419 [48138.1 MB] [10.2%]
> Blocks free total 1636317 [51134.9 MB] [10.9%]
> --------------Correct f_blocks-----------
> f_blocks=1887811
> Blocks free for non superuser 1540419 [48138.1 MB] [81.6%]
> Blocks free total 1636317 [51134.9 MB] [86.7%]
> address@hidden ~]$ 
> address@hidden ~]$ 
> address@hidden ~]$ stat -f /cogcap
>   File: "/cogcap"
>     ID: 0        Namelen: 255     Type: nfs
> Blocks: Total: 1887811    Free: 1636308    Available: 1540411    Size: 32768
> Inodes: Total: 7684096    Free: 7460383   
> address@hidden ~]$ 
> address@hidden ~]$ 
> address@hidden ~]$ df -B 1024K /cogcap
> Filesystem           1M-blocks      Used Available Use% Mounted on
> nfs.cogcap.com:/export/cogcap
>                          58995      7860     48139  15% /cogcap
> address@hidden ~]$ 
> address@hidden ~]$ 
> address@hidden ~]$ strace -e trace=statfs,statfs64 a.out /cogcap > /dev/null
> statfs("/cogcap", {f_type="NFS_SUPER_MAGIC", f_bsize=32768, f_blocks=1887811, 
> f_bfree=1636316, f_bavail=1540419, f_files=7684096, f_ffree=7460383, f_fsid={0, 0}, f_namelen=255, 
> f_frsize=4096}) = 0
> statfs("/cogcap", {f_type="NFS_SUPER_MAGIC", f_bsize=32768, f_blocks=1887811, 
> f_bfree=1636316, f_bavail=1540419, f_files=7684096, f_ffree=7460383, f_fsid={0, 0}, f_namelen=255, 
> f_frsize=4096}) = 0
> address@hidden ~]$ exit
>
> Script done on Mon 20 Nov 2006 11:42:12 AM CST
>
>
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