Hi,

While studying the code and attempting to understand it, we have come up
against certain doubts that have us in a slight fix. We've included the
concerned
 sections of the code below, along with our specific problem in each of
these
 sections. A little pointer in the right direction would be of great help.

(Source file : fsr_xfs_fsr.c)

****** Doubt number 1 ******
(line 331 onwards)
int main()

if (optind < argc) // If the command line input contains the XFS
//filesystem name / file on which xfs_fsr needs to be run on
{
for (; optind < argc; optind++)
{
argname = argv[optind]; // save target which can be file or filesystem
if (lstat64(argname, &sb) < 0)
{ /* This system call returns a stat64 structure, and thus sets
                * all fields in it.
* On success, zero is returned.  On error, -1 is returned,
                * and  errno  is set appropriately.
*/
fprintf(stderr,
_("%s: could not stat: %s: %s\n"),
progname, argname, strerror(errno));
continue;
}
// POSIX macros are defined to check the file type using the st_mode field
if (S_ISLNK(sb.st_mode)) // Check if path(argname) is a
//symbolic link, if so link will be stat-ed and not file
{// Hence  we run stat64() and save the obtained stat structure
struct stat64 sb2;
if (stat64(argname, &sb2) == 0 && (S_ISBLK(sb2.st_mode) ||
     S_ISCHR(sb2.st_mode)))
sb = sb2; // check if stat is a success and
//if argname(path) is block device ? OR is character device?
}
________________________________________________________________________________

We understand that lstat64() and stat64() are used to see if target
 (file/filesystem) can be stated and if yes then the structure is saved.
But we couldn’t exactly understand its use and why both functions are used
separately.
Usually the error could not stat: filename : is followed by Permission
denied.
 Is this related to the root permissions i.e. accessibility ?

****** Doubt number 2 ******

(line 184 onwards)
static char *
find_mountpoint(char *mtab, char *argname, struct stat64 *sb)

while ((t = getmntent(mtabp))) {
if (S_ISDIR(sb->st_mode)) { /* mount point */
if (stat64(t->mnt_dir, &ms) < 0)
continue;
if (sb->st_ino != ms.st_ino)
continue;
if (sb->st_dev != ms.st_dev)
continue;
if (strcmp(t->mnt_type, MNTTYPE_XFS) != 0)
continue;
} else { /* device */
struct stat64 sb2;

if (stat64(t->mnt_fsname, &ms) < 0)
continue;
if (sb->st_rdev != ms.st_rdev)
continue;
if (strcmp(t->mnt_type, MNTTYPE_XFS) != 0)
continue;

/*
 * Make sure the mount point given by mtab is accessible
 * before using it.
 */
if (stat64(t->mnt_dir, &sb2) < 0)
continue;
}
________________________________________________________________________________
We just wanted to confirm if the basic working of the function is
1) To obtain a mount table pointer to the mount table (/etc/mtab/ or
/proc/mounts).
2)  For each entry in the mount table check if it is a directory or device
and after
 performing various comparisons (checks) – (could you please elaborate on
the checks
  performed), this function returns a pointer to the entry.

****** Doubt number 3 ******

(line 677 onwards)
static int
fsrfs(char *mntdir, xfs_ino_t startino, int targetrange)

For the following

__s32 buflenout;

fshandlep = jdm_getfshandle( mntdir );
if ( ! fshandlep ) {
fsrprintf(_("unable to get handle: %s: %s\n"),
          mntdir, strerror( errno ));
return -1;
}
________________________________________________________________________________

We are a bit confused about what is exactly the file handle being returned
 by jdm_getfshandle().
Also what exactly is buflenout. Is it a structure field ?
________________________________________________________________________________

while ((ret = xfs_bulkstat(fsfd,&lastino, GRABSZ, &buf[0], &buflenout) ==
0))
 {
xfs_bstat_t *p;
xfs_bstat_t *endp;

if (buflenout == 0)
goto out0;

/* Each loop through, defrag targetrange percent of the files */
count = (buflenout * targetrange) / 100;

qsort((char *)buf, buflenout, sizeof(struct xfs_bstat), cmp);
________________________________________________________________________________

In the above code snippet we understand that the while loop will run for
N(10)
passes and defragment top 10% of the defragmented files.
However we would appreciate if you could further explain the functions:

(ret = xfs_bulkstat(fsfd,&lastino, GRABSZ, &buf[0], &buflenout) == 0)

qsort((char *)buf, buflenout, sizeof(struct xfs_bstat), cmp);

We know that the sort function will be used to sort extents based on size
and then
offset, but a bit more information on how it is exactly working will be
really
appreciated, as we believe that this sort() has some other purpose.
________________________________________________________________________________



For this mail we have listed only a limited number of doubts that we think
are pressing. Based on further explanations that we might receive from you,
we will send out another  mail for the doubts that still linger.

Regards,
A-DRS.