linux kernel when is file descriptor not accessible by pread?

Question

in line 69, we have:

  /* file can be accessed using pread */
  #define FMODE_PREAD             ((__force fmode_t)8)

I am wondering when would a fd be not accessible by pread? I thought we can do pread on any fd...

Thanks!

Erben

score 1 · Accepted Answer · answered Dec 11 '14 at 00:34

1

man pread on my Linux system says:

The file referenced by fd must be capable of seeking.

So if a file descriptor is not seekable (e.g. a socket or stdin), you will not be able to pread it.

answered Dec 11 '14 at 00:34

John Zwinck

awesome... I was trying to figure out why the fd I created is not accessible to pread. Turns out the fd equals 0. Hence I asked this stupid question. – Erben Mo Dec 11 '14 at 00:43

1 Answers1