From owner-freebsd-fs  Thu Aug 12  0:14: 7 1999
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Date: Tue, 10 Aug 1999 16:32:45 +0200
From: Patrik Sundberg <ps@raditex.se>
To: freebsd-fs@freebsd.org
Subject: mfs and imagefile (/usr/src/sbin/newfs/mkfs.c)
Message-ID: <19990810163402.B10448@radiac.sickla.raditex.se>
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Hi,

I hope this goes to the right forum, otherwise I apologize.

I have been trying to set up a FreeBSD box to avoid disc-writes. This lead
me to use mfs-filesystems for things like /var. In the process of doing this
I wanted to initialize a mfs-fs from an image-file. I thought the -F option
was the way to go, but after testing a bit and reading the source it seems
like when using -F one always gets an empty filesystem - it doesn't care
about the contents of the file given.

We asked Andrzej Bialecki(picobsd) about it and he too thought the -F flag was
the way to accomplish this, but later came to the same conclusion as we did.

The relevant sourcecode (mkfs.c):

if(filename) {
  unsigned char buf[BUFSIZ];
  unsigned long l,l1;
  fd = open(filename,O_RDWR|O_TRUNC|O_CREAT,0644);
  if(fd < 0)
    err(12, "%s", filename);
  for(l=0;l< fssize * sectorsize;l += l1) {
    l1 = fssize * sectorsize;
    if (BUFSIZ < l1)
      l1 = BUFSIZ;
    if (l1 != write(fd,buf,l1))
      err(12, "%s", filename);
  }
  membase = mmap(0,
                 fssize * sectorsize,
                 PROT_READ|PROT_WRITE,
                 MAP_SHARED,
                 fd,
                 0);

  if(membase == MAP_FAILED)
    err(12, "mmap");
  close(fd);
} else {

It makes the file 0 size and then writes an uninitialized buffer to it until
it is of correct size(?).

Is there any reason for not having the possibility to use the contents of
the file to initialize the fs? Maybe we could have a flag which specifies
the behaviour of -F ?

-- 
Patrik Sundberg  -  email: ps@raditex.se - PGP: finger ps@raditex.se
  ---> telefon: 08-636 59 39  -  mobiltelefon: 070-760 22 40 <---


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