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From: Will Drewry on 2 Aug 2010 23:00
EFI's GPT partitioning scheme expects that all partitions have a unique
identifiers. After initial partition scanning, this information is
completely lost to the rest of the kernel.

efi_partition_by_guid exposes GPT parsing support in a limited fashion
to allow other portions of the kernel to map a partition from GUID to
map.

This change is motivated the desire to have the ability to specify a
UUID argument to a device mapper target allowing it to select the device
by the UUID.

Change against Linus's tree: 9fe6206f400646a2322096b56c59891d530e8d51

Signed-off-by: Will Drewry <wad(a)chromium.org>

v2: pr_debug(KERN_WARNING -> pr_debug(. joe(a)perches.com
moved down trailing {. davem(a)davemloft.net
---
fs/partitions/efi.c | 61 +++++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/efi.h | 5 ++++
2 files changed, 66 insertions(+), 0 deletions(-)

diff --git a/fs/partitions/efi.c b/fs/partitions/efi.c
index 9efb2cf..8669c4f 100644
--- a/fs/partitions/efi.c
+++ b/fs/partitions/efi.c
@@ -633,3 +633,64 @@ int efi_partition(struct parsed_partitions *state)
printk("\n");
return 1;
}
+
+/**
+ * efi_partition_by_guid
+ * @bdev: Whole block device to scan for a GPT.
+ * @guid: Unique identifier for the partition to find.
+ *
+ * N.b., returns on the first match since it should be unique.
+ *
+ * Returns:
+ * -1 if an error occurred
+ * 0 if there was no match (or not GPT)
+ * >=1 is the index of the partition found.
+ *
+ */
+int efi_partition_by_guid(struct block_device *bdev, efi_guid_t *guid) {
+ gpt_header *gpt = NULL;
+ gpt_entry *ptes = NULL;
+ u32 i;
+ struct parsed_partitions *state;
+ int part = 0;
+
+ if (!bdev || !guid)
+ return -1;
+
+ state = kzalloc(sizeof(struct parsed_partitions), GFP_KERNEL);
+ if (!state)
+ return -1;
+
+ state->limit = disk_max_parts(bdev->bd_disk);
+ pr_debug("efi_find_partition looking for gpt\n");
+
+ state->bdev = bdev;
+ if (!find_valid_gpt(state, &gpt, &ptes) || !gpt || !ptes) {
+ pr_debug("efi_find_partition no GPT\n");
+ kfree(gpt);
+ kfree(ptes);
+ kfree(state);
+ return 0;
+ }
+
+ pr_debug("GUID Partition Table is valid! Yea!\n");
+ pr_debug("efi_find_partition: 0 -> %d (limit:%d)\n",
+ le32_to_cpu(gpt->num_partition_entries),
+ state->limit);
+ for (i = 0; i < le32_to_cpu(gpt->num_partition_entries) &&
+ i < state->limit-1; i++) {
+ if (!is_pte_valid(&ptes[i], last_lba(bdev)))
+ continue;
+
+ /* Bails on first hit so duped "unique" GUIDs will be FCFS. */
+ if (!efi_guidcmp(ptes[i].unique_partition_guid,
+ *guid)) {
+ part = i + 1;
+ break;
+ }
+ }
+ kfree(ptes);
+ kfree(gpt);
+ kfree(state);
+ return part;
+}
diff --git a/include/linux/efi.h b/include/linux/efi.h
index fb737bc..1a77259 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -301,6 +301,11 @@ extern unsigned long efi_get_time(void);
extern int efi_set_rtc_mmss(unsigned long nowtime);
extern struct efi_memory_map memmap;

+#ifdef CONFIG_EFI_PARTITION
+struct block_device;
+extern int efi_partition_by_guid(struct block_device *bdev, efi_guid_t *guid);
+#endif
+
/**
* efi_range_is_wc - check the WC bit on an address range
* @start: starting kvirt address
--
1.7.0.4

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