[LU-6870] lfs changelog --follow doesn't work

• Type: Bug
• Resolution: Unresolved
• Priority: Minor
• Labels: changelog
• Severity: 3
• Assignee: WC Triage
• Reporter: John Hammond

Description

The llapi changelog internals do not interpret the EOF condition correctly and this breaks 'lfs changelog --follow'.

t:lustre-release# lctl --device lustre-MDT0000 changelog_register
lustre-MDT0000: Registered changelog userid 'cl1'
t:lustre-release# touch /mnt/lustre/f0
t:lustre-release# lfs changelog lustre-MDT0000
1 01CREAT 17:28:22.890999977 2015.07.17 0x0 t=[0x200000404:0x36:0x0] j=touch.0 p=[0x200000007:0x1:0x0] f0
2 11CLOSE 17:28:22.896000006 2015.07.17 0x42 t=[0x200000404:0x36:0x0] j=touch.0
t:lustre-release# lfs changelog --follow lustre-MDT0000
1 01CREAT 17:28:22.890999977 2015.07.17 0x0 t=[0x200000404:0x36:0x0] j=touch.0 p=[0x200000007:0x1:0x0] f0
2 11CLOSE 17:28:22.896000006 2015.07.17 0x42 t=[0x200000404:0x36:0x0] j=touch.0
Unknown changelog message type 0:0

Changelog: Protocol error

Moreover, since the client side changelogf implementation does not offer blocking reads the llapi handler needs to add a short sleep so that we don't tie up a CPU by spinning on an empty pipe.