Date: Wed, 15 Jun 2022 01:50:13 +0000
From: HAGIO KAZUHITO(?????)  <k-hagio-ab@nec.com>
To: "lijiang@redhat.com" <lijiang@redhat.com>,
        "crash-utility@redhat.com" <crash-utility@redhat.com>
Subject: [Crash-utility] [PATCH] Fix for "dev" command on Linux 5.11
        and later
Message-ID: <1655257808-3245-1-git-send-email-k-hagio-ab@nec.com>
Content-Type: text/plain; charset="iso-2022-jp"

The following kernel commits eventually removed the bdev_map array in
Linux v5.11 kernel:

  e418de3abcda ("block: switch gendisk lookup to a simple xarray")
  22ae8ce8b892 ("block: simplify bdev/disk lookup in blkdev_get")

Without the patch, the "dev" command fails to dump block device data
with the following error:

  crash> dev
  ...
  dev: blkdevs or all_bdevs: symbols do not exist

To get block device's gendisk, search blockdev_superblock.s_inodes
instead of bdev_map.

Signed-off-by: Kazuhito Hagio <k-hagio-ab@nec.com>
---
 dev.c | 76 +++++++++++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 71 insertions(+), 5 deletions(-)

diff --git a/dev.c b/dev.c
index db97f8aebdc2..238dfe0fbe3c 100644
--- a/dev.c
+++ b/dev.c
@@ -24,6 +24,7 @@ static void dump_blkdevs_v2(ulong);
 static void dump_blkdevs_v3(ulong);
 static ulong search_cdev_map_probes(char *, int, int, ulong *);
 static ulong search_bdev_map_probes(char *, int, int, ulong *);
+static ulong search_blockdev_inodes(int, ulong *);

 static void do_pci(void);
 static void do_pci2(void);
 static void do_io(void);
@@ -493,9 +494,10 @@ dump_blkdevs(ulong flags)
                 ulong ops;
         } blkdevs[MAX_DEV], *bp;

-       if (kernel_symbol_exists("major_names") &&
-           kernel_symbol_exists("bdev_map")) {
-                dump_blkdevs_v3(flags);
+       if (kernel_symbol_exists("major_names") &&
+           (kernel_symbol_exists("bdev_map") ||
+            kernel_symbol_exists("blockdev_superblock"))) {
+               dump_blkdevs_v3(flags);
                return;
        }

@@ -717,6 +719,7 @@ dump_blkdevs_v3(ulong flags)
        char buf[BUFSIZE];
        uint major;
        ulong gendisk, addr, fops;
+       int use_bdev_map = kernel_symbol_exists("bdev_map");

        if (!(len = get_array_length("major_names", NULL, 0)))
                len = MAX_DEV;
@@ -745,8 +748,11 @@ dump_blkdevs_v3(ulong flags)
                strncpy(buf, blk_major_name_buf + 
                        OFFSET(blk_major_name_name), 16);

-               fops = search_bdev_map_probes(buf, major == i ? major : i,
-                       UNUSED, &gendisk);
+               if (use_bdev_map)
+                       fops = search_bdev_map_probes(buf, major == i ? major : i,
+                               UNUSED, &gendisk);
+               else /* v5.11 and later */
+                       fops = search_blockdev_inodes(major, &gendisk);

                if (CRASHDEBUG(1))
                        fprintf(fp, "blk_major_name: %lx block major: %d name: %s gendisk: %lx fops: %lx\n",
@@ -829,6 +835,66 @@ search_bdev_map_probes(char *name, int major, int minor, ulong *gendisk)
        return fops;
 }

+/* For bdev_inode.  See block/bdev.c */
+#define I_BDEV(inode) (inode - SIZE(block_device))
+

+static ulong
+search_blockdev_inodes(int major, ulong *gendisk)
+{
+       struct list_data list_data, *ld;
+       ulong addr, bd_sb, disk, fops = 0;
+       int i, inode_count, gendisk_major;
+       char *gendisk_buf;
+
+       ld = &list_data;
+       BZERO(ld, sizeof(struct list_data));
+
+       get_symbol_data("blockdev_superblock", sizeof(void *), &bd_sb);
+
+       addr = bd_sb + OFFSET(super_block_s_inodes);
+       if (!readmem(addr, KVADDR, &ld->start, sizeof(ulong),
+           "blockdev_superblock.s_inodes", QUIET|RETURN_ON_ERROR))
+               return 0;
+
+       if (empty_list(ld->start))
+               return 0;
+
+       ld->flags |= LIST_ALLOCATE;
+       ld->end = bd_sb + OFFSET(super_block_s_inodes);
+       ld->list_head_offset = OFFSET(inode_i_sb_list);
+
+       inode_count = do_list(ld);
+
+       gendisk_buf = GETBUF(SIZE(gendisk));
+
+       for (i = 0; i < inode_count; i++) {
+               addr = I_BDEV(ld->list_ptr[i]) + OFFSET(block_device_bd_disk);
+               if (!readmem(addr, KVADDR, &disk, sizeof(ulong),
+                   "block_device.bd_disk", QUIET|RETURN_ON_ERROR))
+                       continue;
+
+               if (!disk)
+                       continue;
+
+               if (!readmem(disk, KVADDR, gendisk_buf, SIZE(gendisk),
+                   "gendisk buffer", QUIET|RETURN_ON_ERROR))
+                       continue;
+
+               gendisk_major = INT(gendisk_buf + OFFSET(gendisk_major));
+               if (gendisk_major != major)
+                       continue;
+
+               fops = ULONG(gendisk_buf + OFFSET(gendisk_fops));
+               if (fops) {
+                       *gendisk = disk;
+                       break;
+               }
+       }
+

+       FREEBUF(gendisk_buf);
+       return fops;
+}
+
 void
 dump_dev_table(void)
 {
--
2.31.1