# cat /proc/mtd
dev: size erasesize name
mtd0: 00180000 00010000 "uboot"
mtd1: 00020000 00010000 "boot-resource"
mtd2: 00020000 00010000 "env"
mtd3: 00020000 00010000 "env-redund"
mtd4: 00780000 00010000 "boot"
mtd5: 007e0000 00010000 "rootfs"
mtd6: 00ec0000 00010000 "UDISK"
mtd7: 08000000 00020000 "spi0.1"
##
# ubiformat /dev/mtd7
ubiformat: mtd7 (nand), size 134217728 bytes (128.0 MiB), 1024 eraseblocks of 131072 bytes (128.0 KiB), min. I/O size 2048 byt es
libscan: scanning eraseblock 1023 -- 100 % complete
ubiformat: 1024 eraseblocks are supposedly empty
ubiformat: formatting eraseblock 1023 -- 100 % complete
#
#
# ubiattach -m 7
ubi0: attaching mtd7
ubi0: scanning is finished
ubi0: attached mtd7 (name "spi0.1", size 128 MiB)
ubi0: PEB size: 131072 bytes (128 KiB), LEB size: 126976 bytes
ubi0: min./max. I/O unit sizes: 2048/2048, sub-page size 2048
ubi0: VID header offset: 2048 (aligned 2048), data offset: 4096
ubi0: good PEBs: 1024, bad PEBs: 0, corrupted PEBs: 0
ubi0: user volume: 0, internal volumes: 1, max. volumes count: 128
ubi0: max/mean erase counter: 0/0, WL threshold: 4096, image sequence number: 1346078118
ubi0: available PEBs: 1000, total reserved PEBs: 24, PEBs reserved for bad PEB handling: 20
ubi0: background thread "ubi_bgt0d" started, PID 1306
UBI device number 0, total 1024 LEBs (130023424 bytes, 124.0 MiB), available 1000 LEBs (126976000 bytes, 121.0 MiB), LEB size 126976 bytes (124.0 KiB)
#
## ubimkvol /dev/ubi0 -N my_volume -s 120MiB
Volume ID 0, size 991 LEBs (125833216 bytes, 120.0 MiB), LEB size 126976 bytes (124.0 KiB), dynamic, name "my_volume", alignment 1
#
#
# mkdir /mnt/addon
#
# mount -t ubifs ubi0:my_volume /mnt/addon
UBIFS (ubi0:0): default file-system created
UBIFS (ubi0:0): Mounting in unauthenticated mode
UBIFS (ubi0:0): background thread "ubifs_bgt0_0" started, PID 1556
UBIFS (ubi0:0): UBIFS: mounted UBI device 0, volume 0, name "my_volume"
UBIFS (ubi0:0): LEB size: 126976 bytes (124 KiB), min./max. I/O unit sizes: 2048 bytes/2048 bytes
UBIFS (ubi0:0): FS size: 124436480 bytes (118 MiB, 980 LEBs), journal size 6221824 bytes (5 MiB, 49 LEBs)
UBIFS (ubi0:0): reserved for root: 4952683 bytes (4836 KiB)
UBIFS (ubi0:0): media format: w5/r0 (latest is w5/r0), UUID 9052DCCC-6CB7-46AC-8C19-D7589BB974F3, small LPT model
## dd if=/dev/urandom of=/mnt/addon/x1.bin bs=1M count=20
20+0 records in
20+0 records out
#
# dd if=/dev/urandom of=/mnt/addon/x2.bin bs=1M count=20
20+0 records in
20+0 records out
#
#
# dd if=/dev/urandom of=/mnt/addon/x3.bin bs=1M count=70
70+0 records in
70+0 records out
## md5sum /mnt/addon/*
e6b65f9c308d919a9fd15df47ce8f938 /mnt/addon/x1.bin
ec0d0d20e1ca4937638570313959467d /mnt/addon/x2.bin
875826b16155aed227790c07d0bcee66 /mnt/addon/x3.bin
#离线
modprobe spinand
ubiattach -m 7
mount -t ubifs ubi0:my_volume /mnt/addon
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可惜了，ubifs 不支持swap：A failed attempt：ubifs+swap
# dd if=/dev/zero of=/mnt/swap/swapfile bs=1M count=32
32+0 records in
32+0 records out
33554432 bytes (32.0MB) copied, 0.341635 seconds, 93.7MB/s
# mkswap /mnt/swap/swapfile
Setting up swapspace version 1, size = 33550336 bytes
UUID=79052343-2d79-4423-925b-455c7e328917
# chmod 0600 //mnt/swap/swapfile
# swapon /mnt/swap/swapfile
[ 1984.581859] swapon: swapfile has holes
swapon: /root/swapfile: swapon failed: Invalid argument能想到的方法都想到了，最后一招就只能是看内核的代码了。其中过程略过，只讲最后的发现。
本次遇到的"swapfile has holes"这个错误信息是由下述代码导致的！
int bmap(struct inode *inode, sector_t *block)
{
if (!inode->i_mapping->a_ops->bmap)
return -EINVAL;
*block = inode->i_mapping->a_ops->bmap(inode->i_mapping, *block);
return 0;
}
EXPORT_SYMBOL(bmap);-EINVAL就是invalid argument!，看来是没有bmap操作！进一步阅读内核UBIFS的代码，得到如下：
const struct address_space_operations ubifs_file_address_operations = {
.readpage = ubifs_readpage,
.writepage = ubifs_writepage,
.write_begin = ubifs_write_begin,
.write_end = ubifs_write_end,
.invalidatepage = ubifs_invalidatepage,
.set_page_dirty = ubifs_set_page_dirty,
#ifdef CONFIG_MIGRATION
.migratepage = ubifs_migrate_page,
#endif
.releasepage = ubifs_releasepage,
};可见，这里的确没有设置bmap操作，所以无论如何都会返回EINVAL。
UBIFS不支持文件方式的swap功能。同时，因为UBI本身（注意和UBIFS的区别）不是块设备(/dev/ubix是字符设备），因此也不能支持块设备的swap功能！
为了在使用UBI/UBIFS的系统里面支持swap功能，需要单独一个MTD分区（MTD有块设备支持），通过块设备的方式来支持swap功能！
离线