linux-ext4 - Re: Files full of zeros with coreutils-8.11 and xfs (FIEMAP related?)

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Date:	Thu, 14 Apr 2011 18:48:11 +0200
From:	Markus Trippelsdorf <markus@...ppelsdorf.de>
To:	Eric Sandeen <sandeen@...deen.net>
Cc:	Yongqiang Yang <xiaoqiangnk@...il.com>,
	Pádraig Brady <P@...igbrady.com>,
	xfs-oss <xfs@....sgi.com>, linux-ext4@...r.kernel.org,
	coreutils@....org
Subject: Re: Files full of zeros with coreutils-8.11 and xfs (FIEMAP related?)

On 2011.04.14 at 11:31 -0500, Eric Sandeen wrote:
> On 4/14/11 11:28 AM, Markus Trippelsdorf wrote:
> 
> <snip>
> 
> > Yes, but we're still trying to find out what caused the zeros in the
> > binaries that coreutils installed on my system.
> > 
> > Now the failure only happens when I use "gold" as my linker. With GNU ld
> > everything is OK. But I thought this must be a timing issue, because
> > gold is faster and the binaries in coreutils-8.11/src are all fine.
> 
> maybe xfs_bmap (or filefrag) of the binaries with both linkers would be instructive; are they laid out significantly differently?
> 
> does gold preallocate?

Just checked and yes it does. That should explain the issue I was
seeing.

bool
Output_file::map_no_anonymous()
{
  const int o = this->o_;

  // If the output file is not a regular file, don't try to mmap it;
  // instead, we'll mmap a block of memory (an anonymous buffer), and
  // then later write the buffer to the file.
  void* base;
  struct stat statbuf;
  if (o == STDOUT_FILENO || o == STDERR_FILENO
      || ::fstat(o, &statbuf) != 0
      || !S_ISREG(statbuf.st_mode)
      || this->is_temporary_)
    return false;

  // Ensure that we have disk space available for the file.  If we
  // don't do this, it is possible that we will call munmap, close,
  // and exit with dirty buffers still in the cache with no assigned
  // disk blocks.  If the disk is out of space at that point, the
  // output file will wind up incomplete, but we will have already
  // exited.  The alternative to fallocate would be to use fdatasync,
  // but that would be a more significant performance hit.
  if (::posix_fallocate(o, 0, this->file_size_) < 0)
    gold_fatal(_("%s: %s"), this->name_, strerror(errno));

  // Map the file into memory.
  base = ::mmap(NULL, this->file_size_, PROT_READ | PROT_WRITE,
		MAP_SHARED, o, 0);

  // The mmap call might fail because of file system issues: the file
  // system might not support mmap at all, or it might not support
  // mmap with PROT_WRITE.
  if (base == MAP_FAILED)
    return false;

  this->map_is_anonymous_ = false;
  this->base_ = static_cast<unsigned char*>(base);
  return true;
}


-- 
Markus
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