Re: d_off field in struct dirent and 32-on-64 emulation

On Thu, Dec 27, 2018 at 06:18:19PM +0100, Florian Weimer wrote:

We have a bit of an interesting problem with respect to the d_off
field in struct dirent.

When running a 64-bit kernel on certain file systems, notably ext4,
this field uses the full 63 bits even for small directories (strace -v
output, wrapped here for readability):

getdents(3, [
  {d_ino=1494304, d_off=3901177228673045825, d_reclen=40, d_name="authorized_keys", d_type=DT_REG},
  {d_ino=1494277, d_off=7491915799041650922, d_reclen=24, d_name=".", d_type=DT_DIR},
  {d_ino=1314655, d_off=9223372036854775807, d_reclen=24, d_name="..", d_type=DT_DIR}
], 32768) = 88

When running in 32-bit compat mode, this value is somehow truncated to
31 bits, for both the getdents and the getdents64 (!) system call (at
least on i386).

Why getdents64 system call is affected by this truncation,
isn't it a kernel bug that has to be fixed in the kernel instead?


-- 
ldv