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Suspend, Resume, and Migration in Java Integrating PDF417 in Java Suspend, Resume, and Migration




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Suspend, Resume, and Migration use tomcat barcode pdf417 creator todisplay pdf-417 2d barcode in java Typical 2D QR Code Most guests will want to sup j2ee pdf417 port suspending and resuming. These operations allow the domain to be serialized to disk and then restored later. The machine on which the domain is restored might not even be the same one on which it was suspended.

It must meet the following requirements to be restored: The CPU type must be the same. The new host must have enough free RAM. The block device (if one is in use) must be available.

. 7 Real or virtualized. 5.8. Exercise: Mapping the Shared Info Page It is possible, for example, PDF 417 for Java to have a block device backed by a partition on a USB Flash drive, and suspend the VM to another partition. The drive could then be carried to a new machine and resumed. It is possible that this kind of migration might cause some problems for a guest, because it will need to reinitialize any network interfaces, and will be likely to suddenly change IP addresses.

This shouldn t be a problem for operating systems that already work in laptop environments, however. The rst step in a suspend operation is for the guest to receive a suspend request via the XenStore. It must then put itself into a state ready for suspension and then issue a hypercall to actually begin the suspend operation.

. CPU Suspension Although not related to memo awt PDF417 ry, and thus not entirely relevant here, it is worth remembering that Xen only suspends the state of the rst virtual CPU. If you are running on multiple CPUs, it is your responsibility to stop the others before suspending. When you resume, you must then reinitialize the virtual CPUs before continuing.

It is likely that any running guest will have references to machine pages stored at various places. After it is suspended and resumed, these will all point to random locations, many of which might not even be owned by the guest and thus will cause faults if they are used. The guest must turn all of these into pseudophysical addresses if it owns the pages, or some more abstract representation if not.

An example of the pages requiring more abstract storage is the set used for communication with virtual devices. After migration, the pages need to be reconnected by the new back end. Some part of the guest must maintain the information required to locate the new provider for the device in the XenStore and reconnect the page.

Other parts of the guest may use a pseudo-physical page reference, as long as they do not attempt to use it until it has been remapped. When the guest resumes, it must do the inverse operation. First, shared pages must be remapped via the grant tables.

Often these are indirect references, so the XenStore page must be reconnected and then this is used to discover the new pages. Finally, any other virtual CPUs must be restarted and execution can continue..

5.8 Exercise: Mapping the Shared Info Page One of the rst things a gue PDF 417 for Java st needs to do is map the shared info page into its own address space. The machine address was passed into the domain via the start. 5. Understanding Xen Memory Management info page, in the start info javabean PDF 417 eld. In the kernel bootstrap we wrote previously, we had reserved space for it, so all we need to do now is update our page tables to incorporate it. To make the preallocated space accessible from C, we need to tell the compiler about it.

We do this by declaring the symbol as extern. The compiler then treats it as valid and, if all goes well, the linker replaces it with the address in the assembly le. The full de nition looks like this:.

extern s h a r e d i n f o t s h a r e d i n f o ;. This is comparatively simple pdf417 2d barcode for Java to do. Because we are only updating a single page table entry, we can simply issue the hypercall as shown in Listing 5.8.

The only ag required is to invalidate the TLB line referring to the update. Listing 5.8: Mapping the shared info page into the pre-prepared space.

1 HYPERVISOR update va mappi ng ( 2 ( u n s i g n e d l o n g ) &s h a r e d i n f o , 3 ( u n s i g n e d l o n g l o n g ) s t a r t i n f o >s h a r e d i n f o , 4 UVMF INVLPG ) ;. After this has completed, th awt PDF417 e guest should be able to use the shared info pointer as it would any other C data structure. Several other pages need to be mapped in this way at start-of-day. These include the XenStore and console driver, provided by the start info structure, and any device-related pages found in the XenStore.

This process must be repeated when the domain is resumed, and so it is typically worth creating a function that maps them all in one go, which can be called when the kernel is booted, and again whenever it is resumed..
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