Messages in this thread | | | Date | Sun, 12 Mar 2023 18:15:42 +0800 | From | Chao Yu <> | Subject | Re: [PATCH] ext4: fix to report fstrim.minlen back to userspace |
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On 2023/3/11 11:18, Theodore Ts'o wrote: > Unfortunately, this patch is not correct. The units of struct > fstrim_range's minlen (here, range->minlen) is bytes.
Oh, that's right, sorry for the mistake.
> > However the minlen variable in ext4_trim_fs is in units of *clusters*. > And so it gets rounded up two places. The first time is when it is > converted into units of a cluster: > > minlen = EXT4_NUM_B2C(EXT4_SB(sb), > range->minlen >> sb->s_blocksize_bits); IIUC, if range->minlen is smaller than block size of ext4, above calculation may return a wrong value, due to it looks EXT4_NUM_B2C() expects a non-zero in-parameter.
So it needs to round up minlen to block size first and then round up block size to cluster size:
minlen = EXT4_NUM_B2C(EXT4_SB(sb), EXT4_BLOCK_ALIGN(range->minlen, sb->s_blocksize_bits));
Or do the conversion at a time as you reminded:
minlen = (range->minlen + EXT4_CLUSTER_SIZE(sb) - 1) >> (sb->s_blocksize_bits + EXT4_CLUSTER_BITS(sb));
> > And the second time is when it is rounded up to the block device's > discard granularity. > > So after that if statement, we need to convert minlen from clusters to > bytes, like so: > > range->minlen = EXT4_C2B(EXT4_SB(sb), minlen) << sb->s_blocksize_bits);
Thanks for the detailed explanation and reminder. :)
Thanks,
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