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smb: client: fix open handle lookup in cifs_open()
When looking up open handles to be re-used in cifs_open(), calling
cifs_get_{writable,readable}_path() is wrong as it will look up for
the first matching open handle, and if @file->f_flags doesn't match,
it will ignore the remaining open handles in
cifsInodeInfo::openFileList that might potentially match
@file->f_flags.
For writable and readable handles, fix this by calling
__cifs_get_writable_file() and __find_readable_file(), respectively,
with FIND_OPEN_FLAGS set.
With the patch, the following program ends up with two opens instead
of three sent over the wire.
```
#define _GNU_SOURCE
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
int main(int argc, char *argv[])
{
int fd;
fd = open("/mnt/1/foo", O_CREAT | O_WRONLY | O_TRUNC, 0664);
close(fd);
fd = open("/mnt/1/foo", O_DIRECT | O_WRONLY);
close(fd);
fd = open("/mnt/1/foo", O_WRONLY);
close(fd);
fd = open("/mnt/1/foo", O_DIRECT | O_WRONLY);
close(fd);
return 0;
}
```
```
$ mount.cifs //srv/share /mnt/1 -o ...
$ gcc test.c && ./a.out
```
Signed-off-by: 
Paulo Alcantara (Red Hat) <pc@manguebit.org>
Reviewed-by: 
ChenXiaoSong <chenxiaosong@kylinos.cn>
Cc: David Howells <dhowells@redhat.com>
Cc: linux-cifs@vger.kernel.org
Signed-off-by: 
Steve French <stfrench@microsoft.com>