bug#7450: cp does not check for errno=EISDIR when target is dangling link

[Alan Curry]

=?UTF-8?Q?=D0=9C=D0=B0=D1=80=D0=BA_?= writes:
> 
> How to reproduce:
> 
> $ ln -s non-exist tgt
[...]
> $ cp /etc/passwd tgt/
> cp: cannot create regular file `tgt/': Is a directory
> 
> Novices can not understand this message :)

The same confusing error message also occurs in the simpler case where the
target is simply any nonexistent name with a trailing slash.

$ ls -ld tgt
ls: cannot access tgt: No such file or directory
$ cp /etc/passwd tgt/
cp: cannot create regular file `tgt/': Is a directory

strace shows this:

open("tgt/", O_WRONLY|O_CREAT|O_EXCL|O_LARGEFILE, 0600) = -1 EISDIR (Is a 
directory)

which I think is just bad kernel behavior. There's no errno (among the
classical errno values anyway) which completely expresses "you tried to creat
something with a trailing slash", but I'd rather see ENOENT or ENOTDIR than
EISDIR.

When this open fails, nothing in sight "Is a directory". The problem is that
tgt/ _would_ be a directory, but since it doesn't exist and isn't about to be
created, "Is a directory" is an overstatement.

cp should dodge this issue by never calling creat with a trailing slash. It
could supply a meaningful error message instead of one that is derived from
an errno.

-- 
Alan Curry