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btrfs-progs: docs: document generic error

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Signed-off-by: David Sterba <dsterba@suse.com>
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David Sterba 2022-03-08 16:59:41 +01:00
parent f1e54a0c09
commit 9091be2a4b
2 changed files with 66 additions and 5 deletions
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9
Documentation/ch-zoned-intro.rst
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@ -21,11 +21,10 @@ Requirements, limitations
* maximum zone size is 8GiB
* mixing zoned and non-zoned devices is possible, the zone writes are emulated,
but this is namely for testing
* the super block is handled in a special way and is at different locations
than on a non-zoned filesystem:
* primary: 0B (and the next two zones)
* secondary: 512GiB (and the next two zones)
* tertiary: 4TiB (4096GiB, and the next two zones)
* the super block is handled in a special way and is at different locations than on a non-zoned filesystem:
* primary: 0B (and the next two zones)
* secondary: 512GiB (and the next two zones)
* tertiary: 4TiB (4096GiB, and the next two zones)
Incompatible features
^^^^^^^^^^^^^^^^^^^^^

62
Documentation/trouble-index.rst
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@ -94,6 +94,68 @@ device that's available for the filesystem but without any other existing block
groups. Before balance starts a check is performed to verify the requested
action is possible. If not, ENOSPC is returned.
Generic errors, errno
---------------------
Note there's a established text message for the errors, though they are used in
a broader sense (eg. error mentions a file but it can be relevant for another
structure). The title of each section uses the nonstandard meaning that is
perhaps more suitable for a filesystem.
ENOENT (No such entry)
^^^^^^^^^^^^^^^^^^^^^^
Common error "no such entry", in general it may mean that some structure hasn't
been found, eg. an entry in some in-memory tree. This becomes a critical
problem when the entry is expected to exist because of consistency of the
structures.
ENOMEM (Not enough memory)
^^^^^^^^^^^^^^^^^^^^^^^^^^
Memory allocation error. In many cases the error is recoverable and the
operation restartable after it's reported to userspace. In critical contexts,
like when a transaction needs to be committed, the error is not recoverable and
leads to flipping the filesystem to read-only. Such cases are rare under normal
conditions. Memory can be artificially limited eg. by cgroups, which may
trigger the condition, which is useful for testing but any real workload should
have resources scaled accordingly.
EINVAL (Invalid argument)
^^^^^^^^^^^^^^^^^^^^^^^^^
This is typically returned from ioctl when a parameter is invalid, ie. unexpected
range, a bit flag not recognized, or a combination of input parameters that
does not make sense. Errors are typically recoverable.
EUCLEAN (Filesystem corrupted)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
The text of the message is confusing "Structure needs cleaning", in reality this
is used to describe a severe corruption condition. The reason of the corruption
is unknown at this point, but some constraint or condition has been violated
and the filesystem driver can't do much. In practice such errors can be observed
on fuzzed images, faulty hardware or misinteraction with other parts of the
operating system.
EIO (Input/output error)
^^^^^^^^^^^^^^^^^^^^^^^^
"Input output error", typically returned as an error from a device that was
unable to read data, or finish a write. Checksum errors also lead to EIO, there
isn't an established error for checksum validation errors, although some
filesystems use EBADMSG for that.
EEXIST (Object already exists)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ENOSPC (No space left)
^^^^^^^^^^^^^^^^^^^^^^
EOPNOTSUPP (Operation not supported)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TODO
----