On 10/18/22 23:13, Mike Snitzer wrote:
...
In the absence of that kind of unification, just use 'errno'.
Mikulas touches on why why using errno isn't useful for DM. And for
DM's device stacking it is hard to know which error spewed to dmesg
(via DMERR, DMCRIT, DMINFO, etc) is relevant to a particular admin
interface issuing the DM ioctl.
So the idea to send the (hopefully useful) error string back up to the
relevant userspace consumer was one task that seemed needed (based on
Milan Broz's various complaints against DM.. which sprang from your
regular remainder that DM's version numbers are broken and need to be
removed/replaced).
Well, when you mention my complaints, I think we are moving from one extreme
to another.
For the error reporting - we use errno values in libcryptsetup everywhere,
so if DM ioctls (through libdevmapper we use) returns proper errno, this is
the minimal solution that helps here.
The problem is that ioctl() are often just translated to -EINVAL.
(Or lost in libdevmapper compatibility layers.)
From the dm-crypt/verity/integrity perspective, ENOMEM, ENODEV (bad block device),
ENOTSUP/ENOENT (for crypto algs not available), EIO for IO error,
EILSEQ for data integrity failure is the basic what we need.
(I perhaps forgot some, I can go through the code if you need it.)
As a bonus, if DM ioctl() returns fixed string that describes user-friendly error
(like: "keysize not compatible" or so) that's all we need
(ti->error strings are already in DM targets).
I have never asked for dynamically allocated error strings in kernel
and I do not know Mikulas' motivation to implement it.
Milan
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