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

Eric Sandeen
2011-04-14T16:45:59Z

On 4/14/11 11:48 AM, Markus Trippelsdorf wrote:
> 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.

Well, mystery solved there, at least!

Now for the fixing part :)

Thanks for checking, at least my view of the world is still intact ;)

-Eric

> 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;
> }