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SubjectRe: access() says EROFS even for device files if /dev is mounted RO
On Wed, 29 Nov 2000, Hugh Dickins wrote:

> On Tue, 28 Nov 2000, Andries Brouwer wrote:
> > On Tue, Nov 28, 2000 at 03:04:31PM +0100, Rogier Wolff wrote:
> >
> > > Ok, so if you read the standard carefully you get a bogus result.
> >
> > Why bogus? Things could have been otherwise, but the important
> > part is that all Unices do things the same way.
>
> Yes, and I think you'll have difficulty, Andries, finding
> any other Unices which interpret the standard as you and
> Linux do: Solaris, HP-UX, UnixWare and OpenServer all allow
> writing to a device node (or FIFO) on read-only filesystem.
>
> Hugh
>

So does Linux. There may be a problem with access(), or a problem
with interpreting what it's supposed to do, but device-files and
FIFOs can be opened for write on a read/only file-system.

Script started on Wed Nov 29 09:14:36 2000
# mount -o remount,ro /alt
# cd /alt
# >foo
bash: foo: Read-only file system
# cd dev
# ls >tty # Write to /dev/tty
FIRE hdb ptybe ptyte sda ttybb ttytb vcs31
GPIB hdb1 ptybf ptytf sda1 ttybc ttytc vcs32
MAKEDEV hdb10 ptyc0 ptyu0 sda10 ttybd ttytd vcs33
MAKEDEV.new hdb11 ptyc1 ptyu1 sda11 ttybe ttyte vcs34
NVRAM hdb12 ptyc2 ptyu2 sda12 ttybf ttytf vcs35
VXI hdb13 ptyc3 ptyu3 sda13 ttyc0 ttyu0 vcs36
[Snipped...]


hda9 ptybd ptytd scd1 ttyba ttyta vcs30
# exit
exit

Script done on Wed Nov 29 09:15:49 2000

Linux `man` states that access() checks, in addition to a file, but
also any "file-system object". However, SunOS 5.5.1 talks about files
only.

It may be that access() is not supposed to be used to check the
accessibility of devices, and that only the Linux man page is incorrect.

Cheers,
Dick Johnson

Penguin : Linux version 2.4.0 on an i686 machine (799.54 BogoMips).

"Memory is like gasoline. You use it up when you are running. Of
course you get it all back when you reboot..."; Actual explanation
obtained from the Micro$oft help desk.


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