Re: [PATCH] btrfs-progs: fix fi du so it works in more cases

["Austin S. Hemmelgarn" <ahferroin7@gmail.com>]

On 2016-03-21 13:40, David Sterba wrote:
> On Mon, Mar 21, 2016 at 08:23:11AM -0400, Austin S. Hemmelgarn wrote:
>> Currently, btrfs fi du uses open_file_or_dir(), which tries to open
>> it's argument with o_RDWR.  Because of POSIX semantics, this fails for
>> non-root users when the file is read-only or is an executable that
>> is being run currently, or for all users (including root) when the
>> filesystem is read-only.  THis results in a somewhat confusing 'Unknown
>> error -1' message when trying to check such files.  Switch to using
>> open_file_or_dir3() with O_RDONLY passed in the flags, as this avoids
>> the limitations listed above, and we have no need to write to the files
>> anyway (and thus shouldn't be opening them writable).
>>
>> Signed-off-by: Austin S. Hemmelgarn <ahferroin7@gmail.com>
>
> Applied, thanks.
>
>> ---
>> Build and runtime tested on x86-64 with glibc.
>>
>> I intend to take the time at some point this week to audit all users of
>> open_file_or_dir() and similarly change any that don't need to write
>> to what they're opening, possibly adding a helper function to do a
>> read-only open.
>
> Thanks. I think using open_file_or_dir3(path, &dirstream, O_RDONLY) is
> ok, no need for a helper.
>
Agreed, especially since this appears to be the only place that used 
open_file_or_dir() that doesn't potentially need write access.