by Roderick W. Smith, rodsmith@rodsbooks.com
Originally written: 4/19/2012; last Web page update: 5/6/2012, referencing rEFInd 0.3.3
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This page is part of the documentation for the rEFInd boot manager. If a Web search has brought you here, you may want to start at the main page.
Beginning with version 0.2.7, rEFInd has been able to load EFI drivers. Although EFI implementations should be able to do this prior to rEFInd's launch, in my experience, most EFI implementations offer such poor control over EFI driver loading that they can't be counted on to do this. Thus, if you want to use EFI drivers, rEFInd's ability to do so can be useful. This page tells you why you might want to use drivers, where you can go to find them, and provides tips on a few specific drivers.
EFI supports drivers, which can activate hardware or filesystems in the pre-boot environment. At the moment, EFI drivers are few and far between; but you can or might want to use them for various reasons:
Note that most of these uses are theoretical, at least to me; I don't know of any specific examples of EFI drivers (available as separate files) for disk controller hardware, network cards, or video cards. Such drivers are often embedded in the firmware of the devices themselves, and should be loaded automatically by the EFI. Chances are good that a few such drivers are available, unknown to me, and more may become available in the future. If you happen to have a device and need support for it under EFI, searching for drivers is certainly worth doing.
To the best of my knowledge, the best reason to want EFI driver support in rEFInd is to provide access to filesystems. Although EFI filesystem driver choices are currently limited, those that are available can help to improve your installation and configuration options, particularly if you've found yourself "boxed in" by awkward installation or bugs, such as the dinky ESP that Ubuntu creates by default or the bug that prevents a Linux kernel with EFI stub loader support from booting from the ESP of at least some Macs.
As a side note, using an ISO-9660 driver can theoretically help you keep the size of a custom Linux boot CD/DVD down to a reasonable value. This is because EFI systems normally boot from optical discs by reading a FAT image file in El Torito format and treating that file as an ESP. If you need to store the kernel both in that file and directly in the ISO-9660 filesystem (to maintain bootability on BIOS systems), that can represent an unwanted extra space requirement. Placing rEFInd and an ISO-9660 driver in the FAT image file should enable you to store the kernel on the disc only once. Unfortunately, my attempts to get this to work have failed to date. When the ISO-9660 driver is loaded from the El Torito image, my test systems seem to allow only one of the two filesystems (the El Torito image's FAT filesystem or the optical disc's ISO-9660 filesystem) to be active; load one and the other goes away. Also, some EFI implementations include ISO-9660 drivers, so you might not need a separate ISO-9660 driver if you're building a disc for a particular computer.
As already noted, I know of no EFI drivers for EFI hardware, aside from those that are built into motherboards' EFI implementations. I do, however, know of a few EFI filesystem drivers:
Most of these cross-project drivers appear to be related. For instance, the ISO-9660 drivers are both based on code written by Christoph Phisterer for rEFIt (although he doesn't seem to have finished and released it in binary form himself).
As you can see, pickings are rather slim. Nonetheless, the drivers that exist are useful for certain purposes. The options could increase in the future, too. Source code to a wide variety of filesystems is available in GRUB Legacy, GRUB 2, Linux, various BSD kernels, and in other projects. Sooner or later somebody's likely to begin porting those drivers to EFI. If you do so, or if you know of additional EFI drivers, please tell me about it, so I can share the information here. Likewise if you know of a source for other EFI drivers—say, for a video card or disk controller card.
Once you've obtained an EFI driver or two, you can install it in rEFInd by creating a subdirectory of the rEFInd directory called drivers—for instance, EFI/refind/drivers, if you've installed rEFInd to EFI/refind on the ESP. Alternatively, you can create a directory of any other name and use the scan_driver_dirs option in refind.conf to tell rEFInd where to look for drivers. Either way, rEFInd attempts to load all the EFI drivers from these directories, so placing your files there and rebooting will do the trick.
rEFInd is likely to take slightly longer to start up when you use drivers, but the effect is likely to be small. On my systems, it's usually just a second or so. This effect could be greater with some drivers or on some systems, though.
I've tested the original rEFIt drivers on a handful of systems. First let me re-emphasize one point: To use rEFIt's ext2fs and ReiserFS drivers on a UEFI-based PC, you must separate the x86 and x86-64 binaries from the "fat" binary format that come in the binary package. You can do this with my thin program.
The rEFIt ext2fs driver works on both ext2fs and ext3fs, but not on ext4fs—at least, not in my one test. (There may be options you can use when creating an ext4 filesystem that would enable the rEFIt ext2fs driver to handle it, but if so I don't know what they are.) The ReiserFS driver is obviously useful only on ReiserFS partitions. (Reiser4 is not supported, as far as I know.) Given that these filesystems are getting a bit on in age by Linux standards, you might do well to use them on a separate Linux /boot partition; however, if you're willing to use ext3fs or ReiserFS on your root (/) filesystem, you can use the rEFIt drivers to read your kernel from it. Note that this assumes you use conventional partitions; to the best of my knowledge, there's no EFI driver for Linux's Logical Volume Manager (LVM) or Redundant Array of Independent Disks (RAID) configurations, so the EFI can't access filesystems stored in these ways.
The ext2fs and ReiserFS drivers work, but they are a bit sluggish—particularly the ext2fs driver. The extent of the problem depends on the computer. In my tests so far, VirtualBox has fared the worse. On it, loading a Linux kernel with EFI stub loader from a FAT partition takes 2 seconds, from the moment of selecting the OS in rEFInd to the moment the kernel messages begin to appear. The equivalent time using ReiserFS is 20 seconds, and with ext2fs it's 200 seconds (that is, 3 minutes and 20 seconds). On a 32-bit Mac Mini, though, the speed problem is much less pronounced—my kernel loads in just 3 seconds from a ReiserFS partition and in 13 seconds from an ext2 filesystem. Times with ext2fs on a UEFI PC with an Intel motherboard were also reasonable, although I didn't record precise values. Nonetheless, if you try the ext2fs driver and it seems to hang, be patient; it may finally boot up. If so, and if the delay is too great for you to accept, you might consider using ReiserFS instead of ext2fs or ext3fs, at least if a change is practical. (For a /boot partition, it almost certainly is practical; you can back it up quite easily, create a fresh filesystem on it, and restore it. You may need to adjust your /etc/fstab entry for a new UUID value, though.)
The Clover EFI Tools ext2fs driver performs much like the rEFIt ext2fs driver, but it doesn't deliver a filesystem label, which makes it less desirable. The NTFS driver from this package is nice and speedy, though, so if for some reason you need to place a boot loader on an NTFS volume, this driver might be worth tracking down.
Although both ext2fs and ReiserFS are case-sensitive, these drivers treat them in a case-insensitive way. Symbolic links work, which opens up possibilities for configuration, such as using a single kernel binary for multiple Linux distributions, with a link in one subdirectory pointing to a file in another directory. (If you try this, though, be sure to use relative links, as in ../otherdist/bzImage.efi, at least if the partition is not Linux's root filesystem.)
copyright © 2012 by Roderick W. Smith
This document is licensed under the terms of the GNU Free Documentation License (FDL), version 1.3.
If you have problems with or comments about this Web page, please e-mail me at rodsmith@rodsbooks.com. Thanks.
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