* util/grub.d/10_kfreebsd.in: Initialize ${kfreebsd_device} as the
kFreeBSD device name, except on ZFS where the filesystem label is
used.
(kfreebsd_entry): On ZFS root, load `opensolaris.ko', `zfs.ko' and
`/boot/zfs/zpool.cache'.
Set mountfrom kernel variable using ${kfreebsd_device}.
Make it even harder to use uninitialized `libzfs_handle' (and
make the interface a bit simpler).
* include/grub/util/misc.h (grub_util_init_libzfs)
(libzfs_handle): Remove.
(grub_get_libzfs_handle): New prototype.
* util/misc.c [HAVE_LIBZFS] (libzfs_handle): Add `static'
attribute.
(grub_util_init_libzfs): Remove.
(grub_get_libzfs_handle): New function.
* kern/emu/getroot.c (find_root_device_from_libzfs): Use
grub_get_libzfs_handle() to obtain a libzfs handle instead of
accessing `libzfs_handle' directly.
* include/grub/emu/misc.h (grub_find_mount_point_from_dir)
(grub_find_zpool_from_mount_point): New function prototypes.
* kern/emu/getroot.c [HAVE_GETFSSTAT]: Move `<sys/mount.h>' to ...
* kern/emu/misc.c [HAVE_GETFSSTAT]: ... here.
* kern/emu/getroot.c (find_mount_point_from_dir): Move to ...
* kern/emu/misc.c (grub_find_mount_point_from_dir): ... this. Remove
`static' attribute.
* kern/emu/getroot.c (find_root_device_from_libzfs): Split code for
finding zpool from mount point into ...
* kern/emu/misc.c (grub_find_zpool_from_mount_point): ... this.
* kern/emu/misc.c (grub_make_system_path_relative_to_its_root): When
requested path is part of a ZFS pool, use
grub_find_zpool_from_mount_point() to detect its filesystem name,
and generate a path with `/fsname@path' syntax.
and GRUB_CMDLINE_XEN_DEFAULT. Recommend setting
GRUB_GFXPAYLOAD_LINUX=text rather than unsetting it in order to
disable gfxpayload.
(Shell-like scripting): Add real content.
(Serial terminal): Suggest `terminal_input serial; terminal_output
serial' rather than putting the two commands on separate lines,
since console input will be inoperative after the first command.
(menuentry): Document --class, --users, and --hotkey options.
(terminfo): Describe what `visually-ordered UTF-8' means (thanks,
Vladimir Serbinenko).
Prevent accidental use of uninitialized libzfs_handle.
* util/grub-probe.c (main): Move grub_util_init_libzfs() call to ...
* kern/emu/getroot.c (find_root_device_from_libzfs): ... here.
* util/misc.c (grub_util_init_libzfs): Make this function idempotent.
* configure.ac: Check for `libzfs.h' and `libnvpair.h'.
* include/grub/util/libnvpair.h: Include `<config.h>'.
[HAVE_LIBNVPAIR_H]: Include `<libnvpair.h>' instead of
declaring libnvpair prototypes ourselves.
* include/grub/util/libzfs.h: Include `<config.h>'.
[HAVE_LIBZFS_H]: Include `<libzfs.h>' instead of
declaring libzfs prototypes ourselves.
(libzfs_handle): Moved to ...
* include/grub/util/misc.h (libzfs_handle): ... here.
Include `<grub/util/libzfs.h>'.
Enable `grub-probe -t device' resolution on ZFS.
* configure.ac: Check for getfsstat(), libzfs and libnvpair.
* include/grub/util/libnvpair.h: New file.
* include/grub/util/libzfs.h: New file.
* kern/emu/getroot.c: Include `<assert.h>' and `<error.h>'.
[HAVE_LIBZFS && HAVE_LIBNVPAIR]: Include `<grub/util/libzfs.h>' and
`<grub/util/libnvpair.h>'.
[HAVE_GETFSSTAT]: Include `<sys/mount.h>'.
(find_mount_point_from_dir): New static function.
[HAVE_LIBZFS && HAVE_LIBNVPAIR] (find_root_device_from_libzfs): New
function.
[HAVE_LIBZFS && HAVE_LIBNVPAIR] (grub_guess_root_device): Use
find_root_device_from_libzfs() before ressorting to find_root_device().
* include/grub/util/misc.h (grub_util_init_libzfs): New function
prototype.
* util/misc.c: Include `<grub/util/libzfs.h>'.
(grub_util_init_libzfs): New function.
[HAVE_LIBZFS] (libzfs_handle): New global variable.
[HAVE_LIBZFS] (fini_libzfs): New static function.
(grub_util_init_libzfs): New function.
* util/grub-probe.c (main): Call grub_util_init_libzfs().
* term/efi/console.c (grub_efi_console_init): New function.
(grub_efi_console_fini): New function.
(grub_console_term_output): Register init and fini methods.
2010-07-20 Colin Watson <cjwatson@ubuntu.com>
Generate device.map in something closer to the old ordering.
* util/deviceiter.c (struct device): New declaration.
(compare_file_names): Rename to ...
(compare_devices): ... this. Sort by kernel name in preference to
the stable by-id name, but keep the latter as a fallback comparison.
Update header comment.
(grub_util_iterate_devices) [__linux__]: Construct and sort an array
of `struct device' rather than of plain file names.
Also-By: Colin Watson <cjwatson@ubuntu.com>
* disk/raid.c (insert_array): Use md/%s to name mdadm 1.x devices,
removing the homehost if present.
* kern/emu/getroot.c (get_mdadm_name) [__linux__]: New function.
(grub_util_get_grub_dev): Use md/%s to name mdadm 1.x devices,
removing the homehost if present.
(grub_util_get_grub_dev) [__linux__]: Get the array name from mdadm
if possible.
* util/i386/pc/grub-setup.c (main): Handle md/* devices.
* disk/dmraid_nvidia.c (grub_dmraid_nv_detect): Add start_sector
parameter. Set its pointer target to 0.
* disk/mdraid_linux.c (grub_mdraid_detect): Add start_sector
parameter. Set its pointer target to 0 for 0.9 metadata, or to the
`data_offset' value from the superblock for 1.x metadata.
* disk/raid.c (grub_raid_read): Offset reads by the start sector of
data on the device.
(insert_array): Record the start sector of data on the device.
(grub_raid_register): Pass start_sector parameters to
grub_raid_list->detect and insert_array.
* include/grub/raid.h (struct grub_raid_array): Add start_sector
member.
(struct grub_raid): Add start_sector parameter to `detect'.
* disk/mdraid_linux.c (struct grub_raid_super_1x): Remove
__attribute__ ((packed)), leaving a comment.
(grub_mdraid_detect): Split out 0.9 and 1.x detection to ...
(grub_mdraid_detect_09): ... here and ...
(grub_mdraid_detect_1x): ... here.
2010-07-20 Peter Henn <peter.henn@web.de>
* disk/mdraid_linux.c (grub_mdraid_detect): Fix calculation of 1.x
chunk size and disk size, which are already given as sector counts
as distinct from the 0.90 units. Fetch the correct device number
from the role table instead of using the table index.
2010-07-20 Felix Zielcke <fzielcke@z-51.de>
* disk/dmraid_nvidia.c (grub_dmraid_nv_detect): Set array->name to NULL.
* disk/mdraid_linux.c (grub_raid_super_1x): New structure.
(WriteMostly1): New macro.
Set array->name to NULL for metadata format 0.90. Add support for
metadata 1.x. Fix some comments.
* disk/raid.c (): Add support for name based RAID arrays. Fix a
few comments.
* util/getroot.c (grub_util_get_grub_dev): Add support for
/dev/md/name style devices.
Also-By: Peter Henn <peter.henn@web.de>
Also-By: Colin Watson <cjwatson@ubuntu.com>
Reported and tested by: Aleš Nesrsta.
* disk/ata.c (grub_atapi_close): Removed. All users updated.
(grub_atapi_dev): Changed .name to "ata". New field .id.
* disk/usbms.c (grub_usbms_close): Removed. All users updated.
(grub_usbms_dev): New field .id.
* disk/scsi.c (grub_scsi_iterate): Generate name.
(grub_scsi_open): Parse name.
* include/grub/scsi.h (grub_make_scsi_id): New function.
(grub_scsi_dev): Change iterate and open to number instead of naming
busses. All users updated.
(grub_scsi): Remove name. Add .bus.
(GNU/Linux): Update for GRUB 2.
(Serial terminal): Remove mention of --disable-serial, which was a
GRUB Legacy configure option. Update instructions to use
`terminal_input' and `terminal_output' rather than `terminal'.
(Vendor power-on keys): Copy-edit. Add cross-references to `Simple
configuration' and `Installing GRUB using grub-install'.
(Menu entry editor): Update for GRUB 2.
(terminfo): Add vt100-color, ieee1275, and dumb terminal types.
Document new -a, -u, and -v options.
(initrd): New section.
(initrd16): New section.
(linux): New section.
(linux16): New section.
(search): The `var' argument to `--set' is optional.
(GRUB only offers a rescue shell): Go into a little more detail on
drive ordering.
install_prefix, in line with install_dos_part and install_bsd_part.
Add new prefix variable, which is copied to install_prefix after
comparing core.img in memory with the one read from disk in the
no-embedding case, and use that rather than overwriting
install_prefix immediately when installing to a partition.
Fixes Debian bug #586621; based on patches by Matt Kraai and M. Vefa
Bicakci.
suitable for using within the format argument of printf when
converting grub_size_t.
* disk/usbms.c (grub_usbms_transfer): Use PRIxGRUB_SIZE rather than
"x" to convert grub_size_t arguments.
* kern/efi/efi.c (grub_reboot): Don't return, even if reset_system
fails.
(grub_halt): Likewise.
* kern/ieee1275/openfw.c (grub_reboot): Don't return, even if
reset-all fails.
(grub_halt): Don't return, even if all of shut-down, power-off, and
poweroff fail.
2010-07-01 Vladimir Serbinenko <phcoder@gmail.com>
* disk/lvm.c (grub_lvm_checkvalue): New function.
(grub_lvm_check_flag): Likewise.
Also-By: Vladimir Serbinenko <phcoder@gmail.com>
* kern/emu/hostdisk.c (convert_system_partition_to_system_disk):
Support 'p' as partition separator on kernel of FreeBSD (used
with GPT labels).
(grub_util_biosdisk_get_grub_dev): Likewise.
PATH when running help2man and then run it on the unadorned
executable names, rather than passing $(builddir)/* paths to
help2man. This avoids the build directory ending up in generated
manual pages.
* util/grub-mkconfig.in: Export `GRUB_BADRAM' variable.
* util/grub.d/00_header.in: When `GRUB_BADRAM' is set, issue badram
command using ${GRUB_BADRAM} as parameter.
possible on Linux.
* util/deviceiter.c (check_device): Rename to ...
(check_device_readable_unique): ... this. Update all callers.
Maintain and check a list of which devices (by canonicalized name)
have already been seen.
(clear_seen_devices): New function.
(compare_file_names) [__linux__]: New function.
(grub_util_iterate_devices): Clear the list of seen devices on exit
and (just in case) on entry.
(grub_util_iterate_devices) [__linux__]: Iterate over non-partition
devices in /dev/disk/by-id/, in sorted order. Remove DM-RAID
seen-devices list, superseded by general code in check_device.
(grub_cmd_cat): Parse options. If the --dos option is given, print
DOS-style "\r\n" line endings as simple newlines (Debian bug
#586358).
(GRUB_MOD_INIT): Use extcmd.
(GRUB_MOD_FINI): Likewise.
* docs/grub.texi (cat): Document --dos.
field position and mask size to red fields from mode_info, not
green.
* loader/multiboot_mbi2.c (retrieve_video_parameters): Likewise.
Remove redundant tag->common.framebuffer_type assignment.
Reported by: Seth Goldberg.
change of 2010-01-09, "Make loader output a bit more user-friendly".
* loader/i386/efi/linux.c (grub_linux_boot): Move debug info to
grub_dprintf().
(grub_cmd_linux): Likewise.
(grub_cmd_initrd): Likewise.
* loader/i386/ieee1275/linux.c (grub_cmd_linux): Likewise.
* loader/i386/pc/linux.c (grub_cmd_linux): Likewise.
* kern/i386/qemu/mmap.c (QEMU_CMOS_MEMSIZE2_HIGH): New const.
(QEMU_CMOS_MEMSIZE2_LOW): Likewise.
(grub_lower_mem): Removed.
(grub_upper_mem): Likewise.
(mem_size): Made static.
(above_4g): New variable.
(grub_machine_mmap_init): Detect small mem_size and above_4g.
(grub_machine_mmap_iterate): Order in ascending order and add above_4g
support.
setting GRUB_VIDEO_BACKEND. Make it available as a user override
instead. Replace the gfxterm backend check with a check that
${GRUB_PREFIX}/video.lst is non-empty.
* util/grub.d/00_header.in: Use GRUB_PREFIX rather than computing it
again.
(load_video): New generated function. Call it before loading
gfxterm rather than loading ${GRUB_VIDEO_BACKEND}.
* util/grub.d/10_linux.in (linux_entry): Call load_video.
* util/grub.d/30_os-prober.in (osx_entry): Likewise.
* docs/grub.texi (Simple configuration): Document
GRUB_VIDEO_BACKEND.
Use video functions in linux and xnu loaders.
* conf/i386-pc.rmk (xnu_mod_SOURCES): Remove loader/i386/pc/xnu.c.
* conf/x86-efi.rmk (xnu_mod_SOURCES): Remove loader/i386/efi/xnu.c.
* include/grub/i386/xnu.h (grub_xnu_set_video): Removed.
* loader/i386/efi/linux.c (grub_linux_setup_video): Copied from
loader/i386/pc/linux.c.
(grub_linux_boot): Resynced with loader/i386/pc/linux.c.
(find_line_len): Removed.
(find_framebuf): Likewise.
(grub_cmd_linux): Declare grub_linux_boot as possibly returning.
* loader/i386/efi/xnu.c: Removed.
* loader/i386/pc/xnu.c: Moved from here...
* loader/i386/xnu.c: ...here.
Enable priorities in video drivers.
* include/grub/video.h (grub_video_adapter_prio_t): New type.
(grub_video_adapter): New field prio.
(grub_video_register): Respect prio when inserting.
* video/efi_gop.c (grub_video_gop_adapter): Add prio.
* video/efi_uga.c (grub_video_uga_adapter): Likewise.
* video/emu/sdl.c (grub_video_sdl_adapter): Likewise.
* video/i386/pc/vbe.c (grub_video_vbe_adapter): Likewise.
* video/i386/pc/vga.c (grub_video_vga_adapter): Likewise.
* video/ieee1275.c (grub_video_ieee1275_adapter): Likewise.
* video/sm712.c (grub_video_sm712_adapter): Likewise.
Fix SDL driver ID.
* include/grub/video.h (grub_video_driver_id_t): New value
GRUB_VIDEO_DRIVER_SDL.
* video/emu/sdl.c (grub_video_sdl_adapter): Add id.
Also-By: Vladimir Serbinenko <phcoder@gmail.com>
#585068). Note that the case where the core image is booted using
multiboot and relocated from its original location still requires
more work.
* kern/i386/pc/init.c (make_install_device): If the prefix starts
with "(,", fill the boot drive in between those two characters, but
expect that a full partition specification including partition map
names will follow.
* util/i386/pc/grub-setup.c (setup): Unless an explicit prefix was
specified, write a prefix without the drive name but including a
full partition specification.
compatibility with older versions (before 2010-06-12) which did the
same. In particular, this makes it easier to ship an update-grub
wrapper which is compatible with that used with GRUB Legacy (Debian
bug #586056).
when generating manual pages.
* docs/man/grub-bin2h.h2m: New file.
* docs/man/grub-editenv.h2m: New file.
* docs/man/grub-fstest.h2m: New file.
* docs/man/grub-install.h2m: New file.
* docs/man/grub-macho2img.h2m: New file.
* docs/man/grub-mkconfig.h2m: New file.
* docs/man/grub-mkdevicemap.h2m: New file.
* docs/man/grub-mkfont.h2m: New file.
* docs/man/grub-mkimage.h2m: New file.
* docs/man/grub-mkpasswd-pbkdf2.h2m: New file.
* docs/man/grub-mkrelpath.h2m: New file.
* docs/man/grub-mkrescue.h2m: New file.
* docs/man/grub-ofpathname.h2m: New file.
* docs/man/grub-pe2elf.h2m: New file.
* docs/man/grub-probe.h2m: New file.
* docs/man/grub-reboot.h2m: New file.
* docs/man/grub-script-check.h2m: New file.
* docs/man/grub-set-default.h2m: New file.
* docs/man/grub-setup.h2m: New file.
(Serial terminal): Refer to `terminal_input' and `terminal_output'
commands, not `terminal'.
(serial): Likewise.
(terminal_input): New section.
(terminal_output): New section.
(uppermem): New section (stub).
(Obtaining and Building GRUB): Refer to Bazaar, not Subversion.
(grub_device_mapper_supported): New function.
* include/grub/emu/misc.h (grub_device_mapper_supported): Add
prototype.
* kern/emu/hostdisk.c (find_partition_start): Check whether
device-mapper is supported before trying to use it.
* util/deviceiter.c (grub_util_iterate_devices): Likewise.
(password): New section.
(password_pbkdf2): New section.
(search): New section.
(Security): New section.
(Troubleshooting): New section, currently very incomplete.
(Invoking grub-mkpasswd-pbkdf2): New section.
(Internals): New section, currently very incomplete.
Finally make USB usable.
* bus/usb/ohci.c (grub_ohci_reg_t): Add missing values.
(GRUB_OHCI_RHUB_PORT_POWER_MASK): New macro.
(GRUB_OHCI_RHUB_PORT_ALL_POWERED): Likewise.
(GRUB_OHCI_REG_FRAME_INTERVAL_FSMPS_MASK): Likewise.
(GRUB_OHCI_REG_FRAME_INTERVAL_FSMPS_SHIFT): Likewise.
(GRUB_OHCI_REG_FRAME_INTERVAL_FI_SHIFT): Likewise.
(GRUB_OHCI_FSMPS): Likewise.
(GRUB_OHCI_PERIODIC_START): Likewise.
(GRUB_OHCI_FRAME_INTERVAL): Likewise.
(GRUB_OHCI_SET_PORT_ENABLE): Likewise.
(GRUB_OHCI_CLEAR_PORT_ENABLE): Likewise.
(GRUB_OHCI_SET_PORT_RESET): Likewise.
(GRUB_OHCI_SET_PORT_RESET_STATUS_CHANGE): Likewise.
* bus/usb/ohci.c (grub_ohci_pci_iter): Various important fixups.
(grub_ohci_transaction): Likewise.
(grub_ohci_transfer): Improve condition detection algorithms.
Handle toggle property. Program the transactions correctly.
Improve error handling. Various important fixups.
(grub_ohci_portstatus): Put register writes in right order.
* bus/usb/uhci.c (grub_free_queue): Compute last_trans.
(grub_uhci_transfer): Don't show "failed" message on success.
* bus/usb/usb.c (grub_usb_set_configuration): Zero-fill whole "toggle"
array.
(grub_usb_device_initialize): Read first 8 bytes of descriptor to
determine its size.
* bus/usb/usbtrans.c (grub_usb_control_msg): Use descdev.maxsize0 even
before initialization is completed. Use IN direction for empty
transfers. Use last_trans and compute toggle.
* include/grub/usbtrans.h (grub_usb_transfer): New field last_trans.
(GRUB_USB_FEATURE_ENDP_HALT): Correct the value.
(GRUB_USB_FEATURE_DEV_REMOTE_WU): Likewise.
(GRUB_USB_FEATURE_TEST_MODE): Likewise.
* include/grub/usb.h (grub_usb_err_t): New value GRUB_USB_ERR_UNRECOVERABLE.
(grub_usb_device): Increase toggle to 256.
(grub_usbms_subclass_t): New values GRUB_USBMS_SUBCLASS_RBC,
GRUB_USBMS_SUBCLASS_MMC2, GRUB_USBMS_SUBCLASS_UFI and
GRUB_USBMS_SUBCLASS_SFF8070.
* include/grub/scsicmd.h (grub_scsi_test_unit_ready): New structure.
(grub_scsi_inquiry): New member page and alloc_length.
(grub_scsi_request_sense): New structure.
(grub_scsi_request_sense_data): Likewise.
(grub_scsi_read_capacity): New fields logical_block_addr, PMI and
control.
* disk/scsi.c (grub_scsi_request_sense): New function.
(grub_scsi_test_unit_ready): Likewise.
(grub_scsi_inquiry): Fill new fields.
(grub_scsi_read_capacity): Likewise.
(grub_scsi_read10): Add request sense at the end.
(grub_scsi_read12): Likewise.
(grub_scsi_write10): Likewise.
(grub_scsi_write12): Likewise.
(grub_scsi_open): Add Test Unit Ready.
* disk/usbms.c (grub_usbms_finddevs): Check configcnt.
Support additional subclasses. Con't clear halt yet. Activate the
proper config. Calculate LUNs correctly.
(grub_usbms_transfer): Various important fixups.
2010-06-02 Vladimir Serbinenko <phcoder@gmail.com>
* bus/pci.c (grub_pci_iterate) [GRUB_MACHINE_MIPS_YEELOONG]: Skip ghosts.
* bus/usb/ohci.c (grub_ohci_portstatus): Handle R/WC correctly.
(grub_ohci_fini_hw): New function.
(grub_ohci_restore_hw): Likewise.
(GRUB_MOD_INIT(ohci)): Register preboot hook.
(GRUB_MOD_FINI(ohci)): Shutdown OHCI.
* term/usb_keyboard.c: Remove include of grub/machine/console.h.
2010-06-02 Vladimir Serbinenko <phcoder@gmail.com>
Dedicated DMA allocations.
* bus/pci.c (grub_memalign_dma32): New function
(grub_dma_free): Likewise.
(grub_dma_get_virt): Likewise.
(grub_dma_get_phys): Likewise.
* bus/usb/ohci.c (grub_ohci): New members hcca_addr and hcca_chunk.
(grub_ohci_pci_iter): Use dma32_alloc.
(grub_ohci_transfer): Likewise.
* bus/usb/usbtrans.c (grub_usb_control_msg): Likewise.
(grub_usb_bulk_readwrite): Likewise.
* include/grub/pci.h: Add declarations.
2010-06-02 Vladimir Serbinenko <phcoder@gmail.com>
CS5536 support.
* bus/cs5536.c: New file.
* bus/usb/ohci.c (grub_ohci_pci_iter): Check for CS5536.
* conf/i386.rmk (pkglib_MODULES): Add cs5536.mod.
(cs5536_mod_SOURCES): New variable.
(cs5536_mod_CFLAGS): Likewise.
(cs5536_mod_LDFLAGS): Likewise.
* conf/mips-yeeloong.rmk (kernel_img_HEADERS): Add cs5536.h and
machine/pci.h.
(kernel_img_SOURCES): Add bus/cs5536.c.
(pkglib_MODULES): Add usb.mod, usbtest.mod, ohci.mod, usbms.mod and
usb_keyboard.mod.
(usb_mod_SOURCES): New variable.
(usb_mod_CFLAGS): New variable.
(usb_mod_LDFLAGS): New variable.
(usbtest_mod_SOURCES): New variable.
(usbtest_mod_CFLAGS): New variable.
(usbtest_mod_LDFLAGS): New variable.
(ohci_mod_SOURCES): New variable.
(ohci_mod_CFLAGS): New variable.
(ohci_mod_LDFLAGS): New variable.
(usbms_mod_SOURCES): New variable.
(usbms_mod_CFLAGS): New variable.
(usbms_mod_LDFLAGS): New variable.
(usb_keyboard_mod_SOURCES): New variable.
(usb_keyboard_mod_CFLAGS): New variable.
(usb_keyboard_mod_LDFLAGS): New variable.
* include/grub/smbus.h: New file.
* include/grub/cs5536.h: New file.
Also-By: Vladimir Serbinenko <phcoder@gmail.com>
per the GNU Coding Standards; this is now too obscure to be worth
documenting.
(QNX): Likewise.
(chainloader): Remove cross-reference to `SCO UnixWare'.
(DOS/Windows): New section, borrowed from GRUB Legacy with details
adjusted for GRUB 2.
(SCO UnixWare): Likewise.
(QNX): Likewise.
(chainloader): Add reference to `Block list syntax'.
(drivemap): New section.
(parttool): New section.
configuration file generation using grub-mkconfig. I've left a slot
for documenting the full shell scripting format but have not yet
started on writing that up.
(Invoking grub-mkconfig): New section.
* kern/emu/getroot.c (find_root_device_from_mountinfo): New
function.
(grub_guess_root_device): Call find_root_device_from_mountinfo
before looking in /dev.
as with real block devices. The Linux world seems to be (at best)
in transition here, and GRUB shouldn't get caught in the middle.
* kern/emu/getroot.c (find_root_device): Follow symbolic links under
/dev/mapper.
return NULL for various reasons even if it has a maximum-length
buffer: for example, there might be a symlink loop, or the path
might exceed PATH_MAX. If this happens, return NULL.
