On 08/08/2014 11:26 AM, John Ferlan wrote:
On 08/08/2014 07:07 AM, Ján Tomko wrote:
On 08/05/2014 04:38 PM, John Ferlan wrote:
https://bugzilla.redhat.com/show_bug.cgi?id=1077068
Check for the NFS FS type being true for a "local" stat of the file to force usage of the 'st_size' value rather than calculating the size using the 'st_blocks' and 'st_blksize'. As described in the stat(2) man page:
"Use of the st_blocks and st_blksize fields may be less portable."
experimentation shows a 10M file could get the following output from stat:
st_size=10485760 st_blocks=88 st_blksize=1048576
resulting in a "44 KiB" value being displayed as the allocation value. While this value does match the "du -s" value of the same file, the "du -b" value shows the "st_size" field. Similarly a long listing of the file shows the 10M size.
Capacity should be the apparent size (what du -b shows, or st_size), while allocation should track the on-disk usage (du, st_blocks * 512).
It looks to me that the values are correct, it's just that posix_fallocate does neither work nor fail on NFS.
Jan
Testing seems to indicate that posix_fallocate() either doesn't work as expected on the target or using the target.path is incorrect...
Before posix_fallocate stat st_blocks=0 st_blksize=1048576 st_size=10485760 lseek end=10485760
posix_fallocate of 10485760 bytes on /home/nfs_pool/target/test-vol1
After posix_fallocate stat st_blocks=88 st_blksize=1048576 st_size=10485760 lseek end=10485760
Hmm... would going at the target be correct in this instance? Same test but use the source path:
Before posix_fallocate stat st_blocks=0 st_blksize=4096 st_size=10485760 lseek end=10485760
posix_fallocate of 10485760 bytes on /home/nfs_pool/nfs-export/test-vol1
After posix_fallocate stat st_blocks=20480 st_blksize=4096 st_size=10485760 lseek end=10485760
...
hmm.... 20480 * 512 = 10485760
# df ... localhost:/home/nfs_pool/nfs-export 140979200 35521536 98273280 27% /home/nfs_pool/target #
Well it's a tangled web that's being weaved... The blksize of the target volume comes from the 'wsize' value in the mount: localhost:/home/nfs_pool/nfs-export on /home/nfs_pool/target type nfs4 (rw,relatime,vers=4.0,rsize=1048576,wsize=1048576,...) Further testing shows if I change the wsize to 4096, then I get what I expect; however, starting at 8192 I'll get decreasingly smaller allocations. So this is a "math problem". So going back to writing via posix_fallocate() to the "/home/nfs_pool/target/test-vol" the "issue" is the blksize of the "source" (nfs-export) is 4096 while the blksize of the "target" (target) is 1048576 (as a result of the nfs mount settings). What "seems" to happen is the posix_fallocate() makes 11 "writes" - I assume because blksize*10 < desired_size (10485760) (instead of <=...). Thus 11 * 4096 = 45056 (bytes) / 1024 = 44 KiB which was displayed. Why all this happens I'm not sure. Bug in posix_fallocate()? Bug in configuration? I have to assume that when this code was first added NFS probably was still using smaller block sizes. Whether anyone has noticed or not beyond the virt-test which discovered the issue - I'm not sure. In any case, does anyone have feedback/thoughts for next steps? I can put together something that avoids posix_fallocate() for the create-as and resize paths. John