sf...@users.sourceforge.net wrote:
> Joe Krahn:
>> Maybe it is an XFS issue for symlinks, but what about cases where
>> st_size is zero for regular non-empty files?
>
> I am confused.
> Your problem may be unrelated to symlink on XFS.
>
> (from your first mail)
> ----------------------------------------------------------------------
> There is a bug in aufs where fstat() returns a st_size value of zero.
> This causes cpio to fail on symlinks because st_size is supposed to be
> the symlink string length. It also causes 'du' to return usage sizes of
> zero unless the "--apparent" option is used.
> ----------------------------------------------------------------------
>
> fstat(2) for symlink returns the data of its target file instead of the
> symlink itself.
>
> $ ln -s real_file symlink
> and run the C program.
> {
> fd = open("symlink");
> fstat(fd)
> }
> Then you will get the data of "real_file" instead of "symlink".
> If you (or cpio) want the data of "symlink", you need to issue
> lstat("symlink").
>
When you do fstat() on a symlink, st_size is supposed to return the
length of the stored symlink-target string, rather than the file data
size. So, if you want to read the symlink string to store it in the
archive as a symlink, you use this function:
ssize_t readlink(const char *path, char *buf, size_t bufsiz);
The proper way to call readlink() is to allocate a string buffer
according to the value of st_size. So, any code that reads the actual
symlink value may fail if st_size is wrong. The command-line "stat" and
other coreutils succeed because they will guess and iteratively increase
bufsiz until readlink succeeds.
Joe
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