Continuing from the state in the previous commit, create an ext4 file
system using the previously created external journal and mount it.
# mke2fs -t ext4 -J device=/dev/sdb1 -L test-ext4 /dev/sdb2
# mount /dev/sdb2 /mnt/2
Did some experimenting with trying to create a second file system using
the same external journal which is already in use.
# mke2fs -t ext4 -J device=/dev/sdb1 -L 2nd-test-ext4 /dev/sdb3
...
/dev/sdb1 is apparently in use by the system; will not make a journal here!
# exit $?
1
Examined the source code of mke2fs and found that it performs an
exclusive read-only open of the named journal block device to check if
it is in use by the system or not [1]. Use the same method in GParted.
Not used alternative method would be to mark the jbd active when the
ext3/4 file system using it is active, but that requires working out the
linkage between them. That can be done using either blkid or dumpe2fs
output but that involves parsing more fields and caching more data so is
much more code than just testing the block device busy status using the
same method which mke2fs uses.
Matching UUIDs via blkid output.
# blkid /dev/sdb1 /dev/sdb2
/dev/sdb1: LABEL="test-jbd" UUID="6e52858e-0479-432f-80a1-de42f9a4093e" TYPE="jbd"
/dev/sdb2: LABEL="test-ext4" UUID="cea5c2cd-b21c-4abf-a497-8c073bb12300" EXT_JOURNAL="6e52858e-0479-432f-80a1-de42f9a4093e" TYPE="ext4"
Matching UUIDs via dumpe2fs output.
# dumpe2fs -h /dev/sdb1 | egrep 'Filesystem UUID|Journal users'
dumpe2fs 1.46.3 (27-Jul-2021)
Filesystem UUID: 6e52858e-0479-432f-80a1-de42f9a4093e
Journal users: cea5c2cd-b21c-4abf-a497-8c073bb12300
# dumpe2fs -h /dev/sdb2 | egrep 'Filesystem UUID|Journal UUID'
dumpe2fs 1.46.3 (27-Jul-2021)
Filesystem UUID: cea5c2cd-b21c-4abf-a497-8c073bb12300
Journal UUID: 6e52858e-0479-432f-80a1-de42f9a4093e
If GParted was going to show the journal to file system linkage in the
UI then doing this would be needed. However so far there has only been
a single reported case of a GParted user using an external journal,
therefore adding the code complexity for this feature is not currently
justified. The simple busy detection method used by mke2fs is all that
is needed.
[1] mke2fs source code
https://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git/
misc/mke2fs.c:main()
check_mount(journal_device, force, _("journal"));
misc/util.c:check_mount()
ext2fs_check_if_mounted(device, &mount_flags);
lib/ext2fs/ismounted.c:ext2fs_check_if_mounted()
ext2fs_check_mount_point(file, mount_flags, NULL, 0);
lib/ext2fs/ismounted.c:ext2fs_check_if_mounted()
if (stat(device, &st_buf) == 0 &&
ext2fsP_is_disk_device(st_buf.st_mode)) {
int fd = open(device, O_RDONLY | O_EXCL);
if (fd >= 0) {
/*
* The device is not busy so it's
* definitelly not mounted. No need to
* to perform any more checks.
*/
close(fd);
*mount_flags = 0;
return 0;
} else if (errno == EBUSY) {
busy = 1;
}
}
Closes#89 - GParted doesn't recognise EXT4 fs journal partition
1950a7a09d