21.08.2021 01:45, Michał Mirosław пишет:

On Thu, Aug 19, 2021 at 01:19:17AM +0300, Dmitry Osipenko wrote:

quoted

Support looking up GPT at a non-standard location specified by a block
device driver.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
---
 block/partitions/efi.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/block/partitions/efi.c b/block/partitions/efi.c
index aaa3dc487cb5..7ca5c4c374d4 100644
--- a/block/partitions/efi.c
+++ b/block/partitions/efi.c

@@ -585,6 +585,8 @@ static int find_valid_gpt(struct parsed_partitions *state, gpt_header **gpt,
 	gpt_header *pgpt = NULL, *agpt = NULL;
 	gpt_entry *pptes = NULL, *aptes = NULL;
 	legacy_mbr *legacymbr;
+	struct gendisk *disk = state->disk;
+	const struct block_device_operations *fops = disk->fops;
 	sector_t total_sectors = get_capacity(state->disk);
 	u64 lastlba;
 

@@ -619,6 +621,16 @@ static int find_valid_gpt(struct parsed_partitions *state, gpt_header **gpt,
         if (!good_agpt && force_gpt)
                 good_agpt = is_gpt_valid(state, lastlba, &agpt, &aptes);
 
+	if (!good_agpt && force_gpt && fops->alternative_gpt_sector) {
+		sector_t agpt_sector;
+		int err;
+
+		err = fops->alternative_gpt_sector(disk, &agpt_sector);
+		if (!err)
+			good_agpt = is_gpt_valid(state, agpt_sector,
+						 &agpt, &aptes);
+	}
+

When alternative_gpt_sector is provided I would expect it to override
the default, not be a fallback for it. But if someone tries to put
a broken (decoy, garbage) GPT at a standard place, current ordering
will prevent overriding it.

This will break devices that have GPT at standard location. If someone
tries to manipulate with GPT entries, then it's a problem of that someone.