ebsnvme-id: open devices in read-only mode

[nmeyerhans]

Description of changes:

Opening block devices in read/write mode triggers a kernel change event, which leads to the child devices (corresponding with the partitions) being deleted and recreated. Opening the fd in read-only mode still provides access to the NVME ioctl() interface, but avoids the unnecessary change event.

Issue #15

Tested on Debian unstable (kernel 5.15, python 3.9.9) and Amazon Linux 2 (kernel 4.14, python 2.7.18):

    admin@ip-10-0-0-75:~/amazon-ec2-utils$ git diff master
    diff --git a/ebsnvme-id b/ebsnvme-id
    index c6a31e2..90979f0 100755
    --- a/ebsnvme-id
    +++ b/ebsnvme-id
    @@ -113,7 +113,7 @@ class ebs_nvme_device:
                                            alen=id_len,
                                            cdw10=1)
     
    -        with open(self.device, "r+") as nvme:
    +        with open(self.device, "r") as nvme:
                 ioctl(nvme, NVME_IOCTL_ADMIN_CMD, admin_cmd)
     
         def ctrl_identify(self):
    admin@ip-10-0-0-75:~/amazon-ec2-utils$ stat --format="%i" /dev/nvme1n1p1
    598
    admin@ip-10-0-0-75:~/amazon-ec2-utils$ sudo python3 ./ebsnvme-id /dev/nvme1n1
    Volume ID: vol-019e7bd5b5b3861a0
    sdf
    admin@ip-10-0-0-75:~/amazon-ec2-utils$ stat --format="%i" /dev/nvme1n1p1
    598

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[rramachand21]

Hi Folks, approx when can this be merged?

[rramachand21]

@fred-lefebvre could you please help review this ?