Re: [PATCH] libata: Whitelist SSDs that are known to properly return zeroes after TRIM

[Phillip Susi <psusi@ubuntu.com>]

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On 01/06/2015 11:15 PM, Dave Chinner wrote:
> (e.g. in ext4 inode tables because mkfs used to zero them) if they 
> haven't been used, so when it reads them it detects that 
> initialisation is needed because the blocks are empty....

No, it knows that the inode table needs initialized because there is a
flag in the group descriptor that says this inode table is still
uninitalized.  It never reads the blocks to see if they are full of
zeros.  mke2fs sets the flag when it does not initialize the table
with zeros, either by direct writes ( which it doesn't do if
lazy_itable_init is true, which it defaults to these days ), or by
discarding the blocks when the device claims to support deterministic
discard that zeros.


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