Theodore Tso wrote:
On Fri, Sep 11, 2009 at 07:57:00PM +0200, Damien Guibouret wrote:
I have looked at the new features provided by ext4 and have a question
on flex_bg information initialization:
into ext4_fill_flex_info function of fs/ext4/super.c (lines 1698, 1700
and 1702 for kernel 2.6.31) doesn't the atomic_set calls be atomic_add
to sum statistics of each group composing a flex group, or do I
misunderstand something ?
Good eye; that's a bug; thanks for pointing that out.
For the extension to manage 48 bits blocks number, I do not see anything
to treat this for resize and bad inodes into kernel or e2fsprogs. For
the resize inode, it is perhaps an incompatibility of this feature with
48 bits blocks number, but for the bad inode ?
There is a plan for how to handle online resizing for > 2^32 block
filesystems, but it hasn't been implemented yet. The basic support
for it is there; that's what the META_BG feature is designed to
support, so existing kernels will be able to deal with resized large
filesystemes. But the code to actually do the on-line resizing hasn't
been implemented yet.
For the bad block inode, the solution is to make it be extent mapped
inode. This also hasn't been implemented yet, but this is a much
simpler one to write. The main reason why we haven't is that modern
disks rarely have system-visible bad blocks; normally the hard drive
has its own bad block remapping layer in hardware so we never see a
bad block until the disk is failing so badly it needs to be replaced
ASAP.
- Ted
Hi,
Thanks for the information.
Looking at ext4.h, I think the setting of extra time fields forgets to mask the epoch bits so the
epoch part overwrites nsec part. The second change is only for coherency (2 -> EXT4_EPOCH_BITS):
--- fs/ext4/ext4.h.old 2009-09-12 09:45:42.161490080 +0200
+++ fs/ext4/ext4.h 2009-09-12 09:47:43.808996848 +0200
@@ -481,8 +481,8 @@
static inline __le32 ext4_encode_extra_time(struct timespec *time)
{
return cpu_to_le32((sizeof(time->tv_sec) > 4 ?
- time->tv_sec >> 32 : 0) |
- ((time->tv_nsec << 2) & EXT4_NSEC_MASK));
+ (time->tv_sec >> 32) & EXT4_EPOCH_MASK : 0) |
+ ((time->tv_nsec << EXT4_EPOCH_BITS) & EXT4_NSEC_MASK));
}
static inline void ext4_decode_extra_time(struct timespec *time, __le32 extra)
@@ -490,7 +490,7 @@
if (sizeof(time->tv_sec) > 4)
time->tv_sec |= (__u64)(le32_to_cpu(extra) & EXT4_EPOCH_MASK)
<< 32;
- time->tv_nsec = (le32_to_cpu(extra) & EXT4_NSEC_MASK) >> 2;
+ time->tv_nsec = (le32_to_cpu(extra) & EXT4_NSEC_MASK) >> EXT4_EPOCH_BITS;
}
#define EXT4_INODE_SET_XTIME(xtime, inode, raw_inode) \
Regards,
Damien
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