[LU-12586] truncate to start of uninstantiated PFL component silently fails

Duplicate — Sat, 19 Dec 2020 13:17:24 +0000

Truncate to exactly the first byte of an uninstantiated PFL component doesn't work - It has no effect.

Example:

[root@cent7c02 lustre]# mkdir testdir; lfs setstripe -E 4M --stripe-count=1 -E -1 testdir
[root@cent7c02 lustre]# touch testdir/testfile; lfs getstripe testdir/testfile
testdir/testfile
  lcm_layout_gen:    2
  lcm_mirror_count:  1
  lcm_entry_count:   2
    lcme_id:             1
    lcme_mirror_id:      0
    lcme_flags:          init
    lcme_extent.e_start: 0
    lcme_extent.e_end:   4194304
      lmm_stripe_count:  1
      lmm_stripe_size:   1048576
      lmm_pattern:       raid0
      lmm_layout_gen:    0
      lmm_stripe_offset: 0
      lmm_objects:
      - 0: { l_ost_idx: 0, l_fid: [0x100000000:0x24b:0x0] }    lcme_id:             2
    lcme_mirror_id:      0
    lcme_flags:          0
    lcme_extent.e_start: 4194304
    lcme_extent.e_end:   EOF
      lmm_stripe_count:  1
      lmm_stripe_size:   1048576
      lmm_pattern:       raid0
      lmm_layout_gen:    0
      lmm_stripe_offset: -1[root@cent7c02 lustre]# truncate --size 4194304 testdir/testfile; ls -la testdir/testfile
-rw-r--r-- 1 root root 0 Jul 24 15:11 testdir/testfile
[root@cent7c02 lustre]# truncate --size 4194303 testdir/testfile; ls -la testdir/testfile
-rw-r--r-- 1 root root 4194303 Jul 24 15:11 testdir/testfile
[root@cent7c02 lustre]# truncate --size 4194305 testdir/testfile; ls -la testdir/testfile
-rw-r--r-- 1 root root 4194305 Jul 24 15:11 testdir/testfile

Notice that the truncate to 4 MiB (4194304) leaves the size at 0, but truncate to 4194303 or 4194305 works fine.

Once the component is instantiated, this works fine:

[root@cent7c02 lustre]# truncate --size 4194305 testdir/testfile; ls -la testdir/testfile
-rw-r--r-- 1 root root 4194305 Jul 24 15:14 testdir/testfile
[root@cent7c02 lustre]# lfs getstripe testdir/testfile
testdir/testfile
  lcm_layout_gen:    3
  lcm_mirror_count:  1
  lcm_entry_count:   2
    lcme_id:             1
    lcme_mirror_id:      0
    lcme_flags:          init
    lcme_extent.e_start: 0
    lcme_extent.e_end:   4194304
      lmm_stripe_count:  1
      lmm_stripe_size:   1048576
      lmm_pattern:       raid0
      lmm_layout_gen:    0
      lmm_stripe_offset: 1
      lmm_objects:
      - 0: { l_ost_idx: 1, l_fid: [0x100010000:0x24d:0x0] }    lcme_id:             2
    lcme_mirror_id:      0
    lcme_flags:          init
    lcme_extent.e_start: 4194304
    lcme_extent.e_end:   EOF
      lmm_stripe_count:  1
      lmm_stripe_size:   1048576
      lmm_pattern:       raid0
      lmm_layout_gen:    0
      lmm_stripe_offset: 0
      lmm_objects:
      - 0: { l_ost_idx: 0, l_fid: [0x100000000:0x24e:0x0] }
[root@cent7c02 lustre]# truncate --size 4194304 testdir/testfile; ls -la testdir/testfile
-rw-r--r-- 1 root root 4194304 Jul 24 15:14 testdir/testfile

This is due to a slightly mixup in the write intent code between "end" for truncate, which is a size, and "end" for a normal write, which is actually "endpos", ie, the position of the write cursor after a write, which is not actually accessed and so does not need to be instantiated. But "end" for truncate is not endpos, it's end, ie, it's included.

Fix coming momentarily.

Whamcloud Community JIRA

[LU-12586] truncate to start of uninstantiated PFL component silently fails