On Tue, Apr 15, 2014 at 10:15:01AM +0800, Qu Wenruo wrote: > When using the blkid_get_cache(), things will be cached to reduce the probe > frequency. The question is if you really want to use the cache at all :-) It's pretty common that we have udevd that maintain all necessary information about devices, including information from libblkid. The udev db is the primary source for many system actions and tools. All you need is to use libudev udev_enumerate API to scan for all block devices and udev_device_get_property_value(ID_FS_TYPE). Maybe you can add a new method BTRFS_SCAN_UDEV and use it as default. It would be better to keep libblkid as a fallback solution only. (For very unusual situations where there is no udev or so.) > But filesystem which supports device management like btrfs can remove device > and if fast enough, libblkid will not invalidate the old cache and cause to get > the wrong filesystem type. Well, since commit 6c2f2b9d (year 2010, v2.18), the libblkid uses microsecond resolution to check for device modifications. So the problem is not that btrfs is fast enough ;-) > The bug is describe in the following btrfs patch: > https://patchwork.kernel.org/patch/3960191/ The patch does not make sense at all, blkid without a cache scans /proc/partitions -- so it's almost the same like BTRFS_SCAN_PROC btrfs_scan_block_devices(). > So is there any idea about forcing given cached entry invalidated? It seems you're trying workaround the *btrfs problem*. The command btrfs device delete does not open and modify the device! It uses btrfs ioctl and kernel does the changes to the device. The problem is that kernel does not update atime and mtime of the device. So the changes are completely invisible for libblkid (or another mtime based solutions). See my example below. IMHO it's strange manner to modify files in kernel, but no update mtime. Fortunately kernel at least sends event to udev. Maybe possible workaround is to add utime() call to "btrfs device delete". Something like: diff --git a/cmds-device.c b/cmds-device.c index 309b49e..5c438bf 100644 --- a/cmds-device.c +++ b/cmds-device.c @@ -20,6 +20,8 @@ #include <unistd.h> #include <fcntl.h> #include <sys/ioctl.h> +#include <sys/types.h> +#include <utime.h> #include <errno.h> #include <sys/stat.h> #include <getopt.h> @@ -179,7 +181,8 @@ static int cmd_rm_dev(int argc, char **argv) "ERROR: error removing the device '%s' - %s\n", argv[i], strerror(e)); ret++; - } + } else + utime(argv[i], NULL); } close_file_or_dir(fdmnt, dirstream); BTW, it would be nice to have --verbose option for btrfs-scan, now it seems like black box. Karel See mtime: # stat /dev/sdb2 File: ‘/dev/sdb2’ Size: 0 Blocks: 0 IO Block: 4096 block special file Device: 5h/5d Inode: 392701 Links: 1 Device type: 8,12 Access: (0660/brw-rw----) Uid: ( 0/ root) Gid: ( 6/ disk) Access: 2014-04-15 11:58:58.338758155 +0200 Modify: 2014-04-15 11:58:58.338758155 +0200 Change: 2014-04-15 11:58:58.338758155 +0200 Birth: - # btrfs device add /dev/sdb2 /mnt/test SMALL VOLUME: forcing mixed metadata/data groups # stat /dev/sdb2 File: ‘/dev/sdb2’ Size: 0 Blocks: 0 IO Block: 4096 block special file Device: 5h/5d Inode: 392701 Links: 1 Device type: 8,12 Access: (0660/brw-rw----) Uid: ( 0/ root) Gid: ( 6/ disk) Access: 2014-04-15 11:59:34.930143021 +0200 Modify: 2014-04-15 11:59:34.930143021 +0200 Change: 2014-04-15 11:59:34.930143021 +0200 ^^^^^^^^ # btrfs device delete /dev/sdb2 /mnt/test # stat /dev/sdb2 File: ‘/dev/sdb2’ Size: 0 Blocks: 0 IO Block: 4096 block special file Device: 5h/5d Inode: 392701 Links: 1 Device type: 8,12 Access: (0660/brw-rw----) Uid: ( 0/ root) Gid: ( 6/ disk) Access: 2014-04-15 11:59:34.930143021 +0200 Modify: 2014-04-15 11:59:34.930143021 +0200 Change: 2014-04-15 11:59:34.930143021 +0200 ^^^^^^^^^ -- Karel Zak <kzak@xxxxxxxxxx> http://karelzak.blogspot.com -- To unsubscribe from this list: send the line "unsubscribe util-linux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
