Loop back device12/7/2023 When I open a loop device (/dev/loop*) instead of a tty, epoll_ctl fails with EPERM. Since 3.1 there is /dev/loop-control, and loop devices are allocated dynamically as needed, rather than a fixed number. It works fine with the tty device, however, I want to write test cases for this module. Before kernel 3.1, you had to set a fixed number of loop devices. Here is one answer that seems to work: use the loopback device to create a. This is delivered via the loopback interface back to the ping program, which shows that we got a reply from 10.0.3.2.I am writing a small library module which accesses the UART and uses epoll to react on incoming data. What I need was lightweight transparent compression that works on one directory. Next, the kernel sends a response to the ping: an ICMP response packet with the addresses reversed: 10.0.3.2 as source address and 10.0.3.1 as destination. (In the case of ping, the kernel processes it internally.) We have now received a "remote" ICMP packet with a destination address of 10.0.3.2, which is arguably not one of our local addresses, but it was delivered to the loopback interface nonetheless. From the kernel's point of view, we have now received an incoming packet ready for consumption by a server process listening on a socket. Now, because the packet was given to the lo interface, the loopback interface does what it normally does: it takes the packet off the send queue and puts it on the receive queue. UniPRO SEL 1 Part number R154000 GbE loopback device with single copper and optical ports For use with UniPRO MGig 1 Eliminates need for full fledged. In this case the matching entry is this: local 10.0.3.0/24 dev lo proto kernel scope host src 10.0.3.1, which says the packet should be delivered via the lo interface with the source address 10.0.3.1. Just like with any packet to be delivered, the kernel consults the routing table. If the device is already allocated, the call fails. Multi-output devices allow you to send sound to. loopback testing allows bidirectional testing with a single OTDR from single location, enabling testing of two fibers at the same time using a loopback device. It can wind up being a kind of tricky concept, but it has myriad uses, especially in the days of social distancing. On success, the device index is returned as the result of the call. This is the concept of virtualy routing the audio out from your computer directly to a destination without needing any cables or additional hardware. There may be several mounts at a given time, therefore there's a need to know which loop device is behind which dev mapper device. We will now create a new mount point and verify that the standard file. The purpose of this is an unmount script that by the mount point name unmaps the dev mapper device, and frees the loopback device as well. LOOPCTLADD Add the new loop device whose device number is specified as a long integer in the third ioctl (2) argument. lp prepared such that we can mount it like a ext3 file system via the loop back device. However, the addition of the loopback mechanism, and interaction with the OS filesystem layer, means that IO operations can be slow and resource-intensive. Here is what happens when you ping 10.0.3.2: the kernel gets an IP packet for delivery with a destination address 10.0.3.2. On success, the device number is returned as the result of the call. The loop-lvm mode makes use of a 'loopback' mechanism that allows files on the local disk to be read from and written to as if they were an actual physical disk or block device. This routing table entry tells that a packet sent to any address between 10.0.3.1 and 10.0.3.254 is sent via the lo interface, from which it is immediately returned.ĮDIT: clarification as a response to the comment below. Something like local 10.0.3.0/24 dev lo proto kernel scope host src 10.0.3.1 You can see this with ip route show table local When you add an address on the loopback interface with e.g. When you ping 10.0.3.2, the reply does not come from some external device, but from the loopback interface itself. There is nothing that can change this behaviour of the loopback interface, that's what it is coded to do. It makes little sense to put a default route on the loopback interface, because the only place it can send packets to is the imaginary piece of wire that is looped from the output of the interface to the input. whatever you send to it is received on the interface. The only purpose of the loopback interface is to return the packets sent to it, i.e. The loopback interface is a virtual interface.
0 Comments
Leave a Reply.AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |