[Gluster-devel] Suggestion to optimize posix_getxattr call

Mohit Agrawal moagrawa at redhat.com
Mon May 15 09:26:34 UTC 2017


  I was just checking of posix_getxattr code to debug of my one problem.I
have found scope of improvement in
  this function to execute system call in better way.As of now
function(posix_getxattr) is calling system
  calls (sys_lgetxattr) two times to get the value of xattr or in case of
list of xattr it calls multiple times

 1) In first time it get the buffer size required to store the value.
     call "size = sys_lgetxattr (real_path, key, NULL, 0);"
 2) In second time it calls the sys_lgetxattr with buffer after allocate
the buffer size
     sys_lgetxattr (real_path, key, value, size);

  In the same way function is calling for listxattr also.I think we can
optimise it as like below
  declare buffer buf[8192](size can be double to this also)
  1) Call size = sys_lgetxattr (real_path,key,buf,8192)
  2) if size == -1 and errono == ERANGE then we need to call systemcalls in
old way like above otherwise
     we don't need to do anything.

  In the case of failure we need to call systemcall 3 times while buffer is
more than our declared buffer
  size otherwise in most of the cases we need to call it only once.

    Please share your input on this, appreciate your input.

Mohit Agrawal
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