client: use 4MB f_bsize and f_frsize for statfs

Old stat(1) reports:

  Block size: 1048576    Fundamental block size: 1048576

and the df(1) arithmetic works out.  New stat(1) reports:

  Block size: 1048576    Fundamental block size: 4096

which is what we are shoving into statvfs, but we have the b_size and
fr_size arithmetic swapped.  However, doing the *correct* reporting would
then break the old stat by making both sizes appear to be 4KB (or
whatever).

Sidestep the issue by making *both* values 4MB.. which is both large enough
to report large FS sizes, and also the default stripe size and thus a
"reasonable" value to report for a block size.

Perhaps in the future, when we no longer care about old userland, we can
report the page size for f_bsize, which is probably the "most correct"
thing to do.

Fixes: #3794.  See also #3793.
Signed-off-by: Sage Weil <sage@inktank.com>
Reviewed-by: Greg Farnum <greg@inktank.com>

1 files changed, 8 insertions, 5 deletions

diff --git a/src/client/Client.cc b/src/client/Client.cc
index 2afb88bf1fb..9f1f9aa5d34 100644
--- a/src/client/Client.cc
+++ b/src/client/Client.cc
@@ -6031,17 +6031,20 @@ int Client::statfs(const char *path, struct statvfs *stbuf)
 
   memset(stbuf, 0, sizeof(*stbuf));
 
-  /* we're going to set a block size of 1MB so we can represent larger
-   * FSes without overflowing. Additionally convert the space measurements
-   * from KB to bytes while making them in terms of blocks.
+  /*
+   * we're going to set a block size of 4MB so we can represent larger
+   * FSes without overflowing. Additionally convert the space
+   * measurements from KB to bytes while making them in terms of
+   * blocks.  We use 4MB only because it is big enough, and because it
+   * actually *is* the (ceph) default block size.
    */
-  const int CEPH_BLOCK_SHIFT = 20;
+  const int CEPH_BLOCK_SHIFT = 22;
+  stbuf->f_frsize = 1 << CEPH_BLOCK_SHIFT;
   stbuf->f_bsize = 1 << CEPH_BLOCK_SHIFT;
   stbuf->f_blocks = stats.kb >> (CEPH_BLOCK_SHIFT - 10);
   stbuf->f_bfree = stats.kb_avail >> (CEPH_BLOCK_SHIFT - 10);
   stbuf->f_bavail = stats.kb_avail >> (CEPH_BLOCK_SHIFT - 10);
   stbuf->f_files = stats.num_objects;
-  stbuf->f_frsize = CEPH_PAGE_SIZE;
   stbuf->f_ffree = -1;
   stbuf->f_favail = -1;
   stbuf->f_fsid = -1;       // ??