reflinked file size incorrect

Both cp --reflink and bcp sometimes round the file size up to the next 4k boundary, with the balance consisting of null bytes. At first glance this behavior occurs for source file size > 3916 bytes. I have tried this with stock btrfs from kernel 2.6.35-rc2 and 2.6.35-rc1 -- specifically, Ubuntu 2.6.35-2.3~lucid1-server and 2.6.35-1.1~lucid1-server. Any ideas?

$ rm -f abc; dd if=/dev/urandom of=abc bs=1 count=3917; \
  cp --reflink abc abc.1; ll abc*
3917 bytes (3.9 kB) copied, 0.0380613 s, 103 kB/s
-rw-r----- 1 root root 3917 2010-06-12 04:22 abc
-rw-r----- 1 root root 4096 2010-06-12 04:22 abc.1

$ rm -f abc; dd if=/dev/urandom of=abc bs=1 count=3916; \
  cp --reflink abc abc.1; ll abc*
3916 bytes (3.9 kB) copied, 0.0299729 s, 131 kB/s
-rw-r----- 1 root root 3916 2010-06-12 04:22 abc
-rw-r----- 1 root root 3916 2010-06-12 04:22 abc.1

$ rm -f abc; dd if=/dev/urandom of=abc bs=1 count=4097; \
  cp --reflink abc abc.1; ll abc*
4097 bytes (4.1 kB) copied, 0.0258441 s, 159 kB/s
-rw-r----- 1 root root 4097 2010-06-12 11:08 abc
-rw-r----- 1 root root 8192 2010-06-12 11:08 abc.1

$ uname -a
Linux allie 2.6.35-2-server #3~lucid1-Ubuntu SMP Thu Jun 10 17:52:32 UTC 2010 x86_64 GNU/Linux

Jim

This bug is new in 2.6.35-rc1 from a22285a6 (Btrfs: Integrate metadata reservation with start_transaction). Just sent a patch fixing this up to the list.

sage

At 05:41pm on 2010 June 12, Sage Weil did write:

Thank you, patch works perfectly.
Jim