Messages in this thread | ![/](/images/icornerl.gif) | | Date | Thu, 28 Apr 2005 12:51:46 -0500 | From | Dmitry Torokhov <> | Subject | Re: [RFC/PATCH 0/5] read/write on attribute w/o show/store should return -ENOSYS |
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On 4/28/05, Chris Wright <chrisw@osdl.org> wrote: > * Greg KH (gregkh@suse.de) wrote: > > On Thu, Apr 28, 2005 at 12:30:09AM -0500, Dmitry Torokhov wrote: > > > Hi, > > > > > > Jean Delvare has noticed that if a driver happens to declare its > > > attribute as RW but doesn't provide store() method attempt to write > > > into such attribute will cause spinning process as most of the > > > attribute implementations return 0 in case of missing store causing > > > endless retries. In some cases missing show/store will return -EPERM, > > > -EACCESS or -EINVAL. > > > > > > I think we should unify implementations and have them all return -ENOSYS > > > (function not implemented) when corresponding method (show/store) is > > > missing. > > > > What is the POSIX standard for this? ENOSYS or EACCESS? > > SuSv3 suggests EBADF, however we already do EINVAL at VFS for no write > op. Although, returning 0 (i.e. wrote zero bytes) is still meaningful > too. >
Returning 0 causes caller to immediately repeat operation causing the loop and 100% CPU utiluization as was reported. If ENOSYS is not acceptable (after all the problem is sysfs-specific, other fs-es either support write or they don't for entire volume) I'd say (looking at the descripptions) we should use ENXIO instead of EBADF:
[ENXIO] A request was made of a nonexistent device, or the request was outside the capabilities of the device.
[EBADF] The fildes argument is not a valid file descriptor open for writing.
We have a valid FD and it was opened for wrinting, so EBADF is not really applicable. But then I may be talking complete gibberish...
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