* util/hostdisk.c (struct grub_util_biosdisk_data): New structure.
(grub_util_biosdisk_open): Initialise disk->data.
(struct linux_partition_cache): New structure.
(linux_find_partition): Cache partition start positions; these are
expensive to compute on every read and write.
(open_device): Cache open file descriptor in disk->data, so that we
don't have to reopen it and flush the buffer cache for consecutive
operations on the same device.
(grub_util_biosdisk_close): New function.
(grub_util_biosdisk_dev): Set `close' member.
* conf/common.rmk (grub_probe_SOURCES): Add kern/list.c.
* conf/i386-efi.rmk (grub_setup_SOURCES): Likewise.
* conf/i386-pc.rmk (grub_setup_SOURCES): Likewise.
* conf/sparc64-ieee1275.rmk (grub_setup_SOURCES): Likewise.
* conf/x86_64-efi.rmk (grub_setup_SOURCES): Likewise.
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