参考 http://linux-sunxi.org/USB_Gadget/Mass_storage
make kernel_menuconfig
Device Drivers ---> USB support ---> USB Gadget Support ---> <M> Mass Storage Gadget
在src/linux-3.14/drivers/usb/gadget下生成g_mass_storage.ko
加载：
Creating a sparse file
Use "dd" command‘s "count" and "seek" options to create a 1GB file that will not use storage until it is used:
# dd if=/dev/zero of=/mass_storage bs=1M seek=1024 count=0 # ls -l /mass_storage -rw-r--r-- 1 root root 1073741824 Feb 15 16:40 /mass_storage # du -hs /mass_storage 0 /mass_storage
Partitioning and formatting sparse file
To be recognized by most Operating Systems, create a single FAT type partition and format it as DOS filesystem using Linux loop device driver.
Create a single partition
# cat <<EOT | sfdisk --in-order -L -uM /mass_storage ,,c EOT
Find partition offset
# fdisk -lu /mass_storage Disk /mass_storage: 1073 MB, 1073741824 bytes 139 heads, 8 sectors/track, 1885 cylinders, total 2097152 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00000000 Device Boot Start End Blocks Id System /mass_storage1 1 2097151 1048575+ c W95 FAT32 (LBA)
First partition starts at first sector: offset = 1 * 512 = 512 bytes
Set up loop device
# losetup -o512 /dev/loop0 /mass_storage # losetup -a /dev/loop0: [b302]:14867 (/mass_storage), offset 512
Format device
# apt-get install dosfstools # mkdosfs /dev/loop0
Test device
# mount -t vfat /dev/loop0 /mnt/ # df -h /mnt Filesystem Size Used Avail Use% Mounted on /dev/loop0 1022M 4.0K 1022M 1% /mnt # mount | grep mnt /dev/loop0 on /mnt type vfat (rw,relatime,fmask=0022,dmask=0022,codepage=cp437,iocharset=ascii,shortname=mixed,errors=remount-ro)
Release device
# umount /mnt/ # losetup -d /dev/loop0 # losetup -a
As we can see below, 1GB sparse file is only using 2.1MB storage (size of filesystem metadata):
# du -sh /mass_storage 2.1M /mass_storage # ls -lh /mass_storage -rw-r--r-- 1 root root 1.0G Feb 15 16:54 /mass_storage