block: remove CONFIG_DEBUG_BLOCK_EXT_DEVT

This might have been a neat debug aid when the extended dev_t was
added, but that time is long gone.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210824075216.1179406-3-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

arch/riscv/configs/defconfig

@@ -132,7 +132,6 @@ CONFIG_DEBUG_PLIST=y
 CONFIG_DEBUG_SG=y
 # CONFIG_RCU_TRACE is not set
 CONFIG_RCU_EQS_DEBUG=y
-CONFIG_DEBUG_BLOCK_EXT_DEVT=y
 # CONFIG_FTRACE is not set
 # CONFIG_RUNTIME_TESTING_MENU is not set
 CONFIG_MEMTEST=y

arch/riscv/configs/rv32_defconfig

@@ -127,7 +127,6 @@ CONFIG_DEBUG_PLIST=y
 CONFIG_DEBUG_SG=y
 # CONFIG_RCU_TRACE is not set
 CONFIG_RCU_EQS_DEBUG=y
-CONFIG_DEBUG_BLOCK_EXT_DEVT=y
 # CONFIG_FTRACE is not set
 # CONFIG_RUNTIME_TESTING_MENU is not set
 CONFIG_MEMTEST=y

block/genhd.c

@@ -313,54 +313,19 @@ void unregister_blkdev(unsigned int major, const char *name)
 
 EXPORT_SYMBOL(unregister_blkdev);
 
-/**
- * blk_mangle_minor - scatter minor numbers apart
- * @minor: minor number to mangle
- *
- * Scatter consecutively allocated @minor number apart if MANGLE_DEVT
- * is enabled.  Mangling twice gives the original value.
- *
- * RETURNS:
- * Mangled value.
- *
- * CONTEXT:
- * Don't care.
- */
-static int blk_mangle_minor(int minor)
-{
-#ifdef CONFIG_DEBUG_BLOCK_EXT_DEVT
-	int i;
-
-	for (i = 0; i < MINORBITS / 2; i++) {
-		int low = minor & (1 << i);
-		int high = minor & (1 << (MINORBITS - 1 - i));
-		int distance = MINORBITS - 1 - 2 * i;
-
-		minor ^= low | high;	/* clear both bits */
-		low <<= distance;	/* swap the positions */
-		high >>= distance;
-		minor |= low | high;	/* and set */
-	}
-#endif
-	return minor;
-}
-
 int blk_alloc_ext_minor(void)
 {
 	int idx;
 
 	idx = ida_alloc_range(&ext_devt_ida, 0, NR_EXT_DEVT, GFP_KERNEL);
-	if (idx < 0) {
-		if (idx == -ENOSPC)
-			return -EBUSY;
-		return idx;
-	}
-	return blk_mangle_minor(idx);
+	if (idx == -ENOSPC)
+		return -EBUSY;
+	return idx;
 }
 
 void blk_free_ext_minor(unsigned int minor)
 {
-	ida_free(&ext_devt_ida, blk_mangle_minor(minor));
+	ida_free(&ext_devt_ida, minor);
 }
 
 static char *bdevt_str(dev_t devt, char *buf)

init/do_mounts.c

@@ -432,10 +432,6 @@ retry:
 		printk("Please append a correct \"root=\" boot option; here are the available partitions:\n");
 
 		printk_all_partitions();
-#ifdef CONFIG_DEBUG_BLOCK_EXT_DEVT
-		printk("DEBUG_BLOCK_EXT_DEVT is enabled, you need to specify "
-		       "explicit textual name for \"root=\" boot option.\n");
-#endif
 		panic("VFS: Unable to mount root fs on %s", b);
 	}
 	if (!(flags & SB_RDONLY)) {

lib/Kconfig.debug

@@ -1679,33 +1679,6 @@ config DEBUG_WQ_FORCE_RR_CPU
 	  feature by default.  When enabled, memory and cache locality will
 	  be impacted.
 
-config DEBUG_BLOCK_EXT_DEVT
-	bool "Force extended block device numbers and spread them"
-	depends on DEBUG_KERNEL
-	depends on BLOCK
-	default n
-	help
-	  BIG FAT WARNING: ENABLING THIS OPTION MIGHT BREAK BOOTING ON
-	  SOME DISTRIBUTIONS.  DO NOT ENABLE THIS UNLESS YOU KNOW WHAT
-	  YOU ARE DOING.  Distros, please enable this and fix whatever
-	  is broken.
-
-	  Conventionally, block device numbers are allocated from
-	  predetermined contiguous area.  However, extended block area
-	  may introduce non-contiguous block device numbers.  This
-	  option forces most block device numbers to be allocated from
-	  the extended space and spreads them to discover kernel or
-	  userland code paths which assume predetermined contiguous
-	  device number allocation.
-
-	  Note that turning on this debug option shuffles all the
-	  device numbers for all IDE and SCSI devices including libata
-	  ones, so root partition specified using device number
-	  directly (via rdev or root=MAJ:MIN) won't work anymore.
-	  Textual device names (root=/dev/sdXn) will continue to work.
-
-	  Say N if you are unsure.
-
 config CPU_HOTPLUG_STATE_CONTROL
 	bool "Enable CPU hotplug state control"
 	depends on DEBUG_KERNEL