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

• Type: Bug
• Status: Resolved
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: Lustre 2.13.0, Lustre 2.12.2, Lustre 2.10.8
• Fix Version/s: Lustre 2.14.0
• Severity: 3
• Assignee: Zhenyu Xu
• Reporter: Patrick Farrell (Inactive)

Description

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.