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boot: generalize CDROM terminology to El Torito

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Per UEFI specification §13.3.2, El Torito partition discovery applies to
any block device, not just optical media. Rename
disk_get_part_uuid_cdrom() to disk_get_part_uuid_eltorito() and update
all log messages and comments to say "El Torito" instead of "CDROM" to
reflect this.
This commit is contained in:
Daan De Meyer
2026-04-05 08:17:59 +00:00
parent 4e0eabd401
commit c82cf5662e
2 changed files with 29 additions and 27 deletions
Download Patch File Download Diff File Expand all files Collapse all files

44
src/boot/part-discovery.c
View File

@@ -320,21 +320,23 @@ EFI_STATUS partition_open(const EFI_GUID *type, EFI_HANDLE *device, EFI_HANDLE *
return EFI_SUCCESS;
}
static char16_t* disk_get_part_uuid_cdrom(const EFI_DEVICE_PATH *dp) {
static char16_t* disk_get_part_uuid_eltorito(const EFI_DEVICE_PATH *dp) {
EFI_STATUS err;
assert(dp);
/* When booting from a CD-ROM via El Torito, the device path contains a CDROM node instead of
* a HARDDRIVE node. The CDROM node doesn't carry a partition UUID, so we need to read the GPT
* from the underlying disk to find it. */
/* When booting via El Torito, the device path contains a CDROM node instead of a HARDDRIVE
* node (UEFI specification §10.3.5.2). The CDROM node doesn't carry a partition UUID, so we
* need to read the GPT from the underlying disk to find it. Per §13.3.2, El Torito partition
* discovery applies to any block device, not just optical media (e.g. an ISO image dd'd to a
* USB stick). */
const CDROM_DEVICE_PATH *cdrom = NULL;
for (const EFI_DEVICE_PATH *node = dp; !device_path_is_end(node); node = device_path_next_node(node))
if (node->Type == MEDIA_DEVICE_PATH && node->SubType == MEDIA_CDROM_DP)
cdrom = (const CDROM_DEVICE_PATH *) node;
if (!cdrom) {
log_debug("No CDROM device path node found.");
log_debug("No El Torito device path node found.");
return NULL;
}
@@ -345,7 +347,7 @@ static char16_t* disk_get_part_uuid_cdrom(const EFI_DEVICE_PATH *dp) {
EFI_HANDLE disk_handle;
err = BS->LocateDevicePath(MAKE_GUID_PTR(EFI_BLOCK_IO_PROTOCOL), &remaining, &disk_handle);
if (err != EFI_SUCCESS) {
log_debug_status(err, "Failed to locate disk device for CDROM: %m");
log_debug_status(err, "Failed to locate disk device for El Torito boot: %m");
return NULL;
}
@@ -354,13 +356,13 @@ static char16_t* disk_get_part_uuid_cdrom(const EFI_DEVICE_PATH *dp) {
EFI_BLOCK_IO_PROTOCOL *block_io;
err = BS->HandleProtocol(disk_handle, MAKE_GUID_PTR(EFI_BLOCK_IO_PROTOCOL), (void **) &block_io);
if (err != EFI_SUCCESS) {
log_debug_status(err, "Failed to get block I/O protocol for CDROM disk: %m");
log_debug_status(err, "Failed to get block I/O protocol for El Torito disk: %m");
return NULL;
}
if (block_io->Media->LogicalPartition || !block_io->Media->MediaPresent ||
block_io->Media->LastBlock <= 1) {
log_debug("CDROM disk has unsuitable media (partition=%ls, present=%ls, lastblock=%" PRIu64 ").",
log_debug("El Torito disk has unsuitable media (partition=%ls, present=%ls, lastblock=%" PRIu64 ").",
yes_no(block_io->Media->LogicalPartition),
yes_no(block_io->Media->MediaPresent),
(uint64_t) block_io->Media->LastBlock);
@@ -369,24 +371,24 @@ static char16_t* disk_get_part_uuid_cdrom(const EFI_DEVICE_PATH *dp) {
uint32_t iso9660_block_size = block_io->Media->BlockSize;
if (iso9660_block_size < 512 || iso9660_block_size > 4096 || !ISPOWEROF2(iso9660_block_size)) {
log_debug("Unexpected CDROM block size %" PRIu32 ", skipping.", iso9660_block_size);
log_debug("Unexpected El Torito block size %" PRIu32 ", skipping.", iso9660_block_size);
return NULL;
}
EFI_DISK_IO_PROTOCOL *disk_io;
err = BS->HandleProtocol(disk_handle, MAKE_GUID_PTR(EFI_DISK_IO_PROTOCOL), (void **) &disk_io);
if (err != EFI_SUCCESS) {
log_debug_status(err, "Failed to get disk I/O protocol for CDROM disk: %m");
log_debug_status(err, "Failed to get disk I/O protocol for El Torito disk: %m");
return NULL;
}
uint32_t media_id = block_io->Media->MediaId;
/* Probe for the GPT header at multiple possible sector sizes (512, 1024, 2048, 4096).
* The GPT header is at LBA 1, i.e. byte offset == sector_size. On CD-ROMs, the GPT
* The GPT header is at LBA 1, i.e. byte offset == sector_size. On El Torito media, the GPT
* may use a different sector size than the media's block size (e.g. 512-byte GPT sectors
* on 2048-byte CD-ROM blocks), so we try all possibilities. If the primary GPT header is
* corrupt but contains a valid backup LBA, fall back to the backup header. */
* on 2048-byte blocks), so we try all possibilities. If the primary GPT header is corrupt
* but contains a valid backup LBA, fall back to the backup header. */
uint32_t gpt_sector_size = 0;
GptHeader gpt;
_cleanup_free_ void *entries = NULL;
@@ -413,18 +415,18 @@ static char16_t* disk_get_part_uuid_cdrom(const EFI_DEVICE_PATH *dp) {
}
if (gpt_sector_size == 0) {
log_debug("No valid GPT found on CDROM at any sector size.");
log_debug("No valid GPT found on El Torito disk at any sector size.");
return NULL;
}
log_debug("Found GPT on CDROM with sector size %" PRIu32 ", %" PRIu32 " partition entries.",
log_debug("Found GPT on El Torito disk with sector size %" PRIu32 ", %" PRIu32 " partition entries.",
gpt_sector_size, gpt.NumberOfPartitionEntries);
/* Find the partition whose byte offset matches the CDROM's PartitionStart.
* CDROM PartitionStart is in media iso9660_block_size units, GPT StartingLBA is in gpt_sector_size units. */
/* Find the partition whose byte offset matches the El Torito PartitionStart.
* El Torito PartitionStart is in media iso9660_block_size units, GPT StartingLBA is in gpt_sector_size units. */
uint64_t cdrom_start;
if (!MUL_SAFE(&cdrom_start, cdrom->PartitionStart, iso9660_block_size)) {
log_debug("CDROM start offset overflow.");
log_debug("El Torito start offset overflow.");
return NULL;
}
@@ -441,7 +443,7 @@ static char16_t* disk_get_part_uuid_cdrom(const EFI_DEVICE_PATH *dp) {
return xasprintf(GUID_FORMAT_STR, GUID_FORMAT_VAL(entry->UniquePartitionGUID));
}
log_debug("No ESP partition matches CDROM start offset %" PRIu64 " (block size %" PRIu32 ").",
log_debug("No ESP partition matches El Torito start offset %" PRIu64 " (block size %" PRIu32 ").",
cdrom->PartitionStart, iso9660_block_size);
return NULL;
}
@@ -470,6 +472,6 @@ char16_t *disk_get_part_uuid(EFI_HANDLE *handle) {
return xasprintf(GUID_FORMAT_STR, GUID_FORMAT_VAL(hd->SignatureGuid));
}
/* No GPT partition node found — try CDROM device path as fallback */
return disk_get_part_uuid_cdrom(dp);
/* No GPT partition node found — try El Torito device path as fallback */
return disk_get_part_uuid_eltorito(dp);
}

12
src/udev/udev-builtin-blkid.c
View File

@@ -426,12 +426,12 @@ static int probe_gpt_boot_disk_needs_loop(UdevEvent *event, int fd) {
sd_device *dev = ASSERT_PTR(ASSERT_PTR(event)->dev);
int r;
/* Probe the GPT sector size. For CD-ROMs booted via El Torito, the GPT may use a different
* sector size than the device (e.g. 512-byte GPT on a 2048-byte CD-ROM). If there's a mismatch,
* check if this is the boot disk by comparing GPT partition UUIDs with the ESP/XBOOTLDR UUID
* exported by the boot loader. If it matches, set a property so that udev rules can set up a
* loop device with the correct sector size — the kernel can't parse the partition table itself
* in this case.
/* Probe the GPT sector size. For devices booted via El Torito, the GPT may use a different
* sector size than the device (e.g. a 512-byte GPT on a device with 2048-byte blocks). If
* there's a mismatch, check if this is the boot disk by comparing GPT partition UUIDs with the
* ESP/XBOOTLDR UUID exported by the boot loader. If it matches, set a property so that udev
* rules can set up a loop device with the correct sector size — the kernel can't parse the
* partition table itself in this case.
*
* Even if the sector sizes match, if the device does not support partition scanning (e.g. some
* CD-ROM drives), the kernel still can't parse the partition table. In that case, if the disk