[PATCH 0/5] btrfs-progs: device_get_partition_size*() enhancement and cleanup

[Qu Wenruo <wqu@suse.com>]

Inspired by recent fixes from Zotan to device_get_partition_size_sysfs(),
it turns out the idea of falling back to use sysfs is not sound in the first
place.

The original issue is unprivileged user can cause `btrfs device usage`
to output incorrect values:

  WARNING: cannot read detailed chunk info, per-device usage will not be shown, run as root
  /dev/mapper/test-scratch1, ID: 1
     Device size:            20.00MiB <<
     Device slack:           16.00EiB <<
     Unallocated:                 N/A

It turns out that, the "unprivileged" part means, the user doesn't have
read access to the raw device.

It's common that a lot of distros have the following mode for raw block
devices:

  brw-rw---- 1 root disk 254, 32 Aug  2 13:35 /dev/vdc

So unprivileged users can not do read access to block devices thus
failed to grab the block device size, and this is normally considered as
a safety method.

But if the end user is inside disk group, everything works fine:

  WARNING: cannot read detailed chunk info, per-device usage will not be shown, run as root
  /dev/mapper/test-scratch1, ID: 1
     Device size:            10.00GiB
     Device slack:              0.00B
     Unallocated:                 N/A

And the original bug is that the sysfs interface only gives the device
size in block unit, and block size can be hard to fetch (partition and
dm have different path to grab the block size).


This makes me wonder, why we need the sysfs interface in the first
place.
If the unprivileged user has no access to a block device, we should
not workaround it, but give a proper error/warning message.

So this series address the root problem, no proper error code for
device_get_partition_size*() helpers.
With proper error handling and messages, we shouldn't even need to use
sysfs to workaround the problem.

With the sysfs fallback removed, a completely unprivileged user will get
the following result:

  WARNING: cannot read detailed chunk info, per-device usage will not be shown, run as root
  WARNING: failed to get device size for devid 1: Permission denied
  /dev/mapper/test-scratch1, ID: 1
     Device size:               0.00B
     Device slack:              0.00B
     Unallocated:                 N/A

Which should give enough for the end user without weird output at all.

Qu Wenruo (5):
  btrfs-progs: remove the unnecessary device_get_partition_size() call
  btrfs-progs: add error handling for device_get_partition_size()
  btrfs-progs: add error handling for
    device_get_partition_size_fd_stat()
  btrfs-progs: remove device_get_partition_size_fd()
  btrfs-progs: remove device_get_partition_size_sysfs()

 check/main.c            |  8 +++-
 check/mode-lowmem.c     |  8 +++-
 cmds/filesystem-usage.c | 11 ++++--
 cmds/replace.c          | 14 ++++++-
 common/device-utils.c   | 87 ++++++++++-------------------------------
 common/device-utils.h   |  5 +--
 image/common.c          |  7 +++-
 kernel-shared/volumes.c |  9 ++++-
 kernel-shared/zoned.c   | 18 ++++++---
 mkfs/common.c           | 16 ++++++--
 mkfs/main.c             | 12 ++++--
 11 files changed, 103 insertions(+), 92 deletions(-)

--
2.50.1