在 Android 的 init.rc 中，可以看到掛載檔案系統使用的 mount 命令，而
這命令和我們一般在 Linux 下使用的 mount 命令不同，是個提供給 init 運作的描
述句，你可以在 system/core/init/builtins.c 找到他的實現。
在大多數的 Android 設備中，常常可以看到掛載 yaffs2 的描述，卻很少看到 ubifs 的掛載描述
mount yaffs2 mtd@system /system
為什麼理應效能比較好的 ubifs 卻未被 Android 系統廣泛使用？個人推測有以下原 因
- 1. Android 採用 yaffs2 作為 MTD NAND Flash 檔案系統
- 2. 大多數的 Android 設備 (ex:手機) 都內建有 emmc 作為儲存空間
實際上在我下載到的 AOSP 原始碼中，init 也看不到有支援 ubifs 的影子，那 我們想讓 Android 的 init 掛載 ubifs 要怎麼辦? 這時候只好自己動手了~
讓 init 可以掛載 ubifs 所進行的修改
Android 的 init 原始碼位於 system/core/init 裡面，為了增加 ubifs 的功
能，我們將針對以下檔案進行修改
- 1. init/builtins.c
- 2. init/util.h
- 3. init/util.c
- 4. init/ubi-user.h
修改 init/builtins.c
我們所希望的是可以在 init.rc 增加下面這樣的描述，讓 init 可以掛載 ubifs
mount ubifs ubi@system /system
要辦到這項功能，我們必須在 system/core/init/builtins.c 裡面加入一
些程式，讓 init 遇到了 ubi@ 這樣的語句時，會去使用 ubi_attach 來去掛載
mtd 設備。
diff --git a/init/builtins.c b/init/builtins.c index b0a97ae..d8066a2 100644 --- a/init/builtins.c +++ b/init/builtins.c @@ -325,6 +325,22 @@ int do_mount(int nargs, char **args) } goto exit_success; + } else if (!strncmp(source, "ubi@", 4)) { + n = ubi_attach_mtd(source + 4); + if (n < 0) { + return -1; + } + + sprintf(tmp, "/dev/ubi%d_0", n); + + if (wait) + wait_for_file(tmp, COMMAND_RETRY_TIMEOUT); + if (mount(tmp, target, system, flags, options) < 0) { + ubi_detach_dev(n); + return -1; + } + + goto exit_success; } else if (!strncmp(source, "loop@", 5)) { int mode, loop, fd; struct loop_info info;
修改 init/util.h
我們在 system/core/init/builtins.c 使用到一些和 ubifs 相關的函式，這
些函式並未被宣告以及定義，因此我們宣告在 util.h 裡面。
diff --git a/init/util.h b/init/util.h index 45905b6..09aa574 100644 --- a/init/util.h +++ b/init/util.h @@ -41,4 +41,7 @@ void get_hardware_name(char *hardware, unsigned int *revision); void import_kernel_cmdline(int in_qemu, void (*import_kernel_nv)(char *name, int in_qemu)); int make_dir(const char *path, mode_t mode); int restorecon(const char *pathname); + +int ubi_attach_mtd(const char *name); +int ubi_detach_dev(int dev); #endif
增加 init/ubi-user.h 檔案
由於我們進行一些 ubifs 相關函式的定義時，需要用到 ubifs 的結構，因此
需要增加相關結構的資訊。 ubi-user.h 這個檔案取自於 Linux Kernel
的 include/mtd/ubi-user.h
請將 Linux Kernel 的 include/mtd/ubi-user.h 複製到 init 目錄裡面，注意到最好
選用你用於 Android 平台的 Linux Kernel 裡面的檔案，因為這個檔案的一些 structure 宣
告可能會因為 Linux Kernel 版本不同而改變。
以下為本文使用的範例:
/* * Copyright © International Business Machines Corp., 2006 * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See * the GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA * * Author: Artem Bityutskiy (Битюцкий Артём) */ #ifndef __UBI_USER_H__ #define __UBI_USER_H__ #include <linux/types.h> /* * UBI device creation (the same as MTD device attachment) * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ * * MTD devices may be attached using %UBI_IOCATT ioctl command of the UBI * control device. The caller has to properly fill and pass * &struct ubi_attach_req object - UBI will attach the MTD device specified in * the request and return the newly created UBI device number as the ioctl * return value. * * UBI device deletion (the same as MTD device detachment) * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ * * An UBI device maybe deleted with %UBI_IOCDET ioctl command of the UBI * control device. * * UBI volume creation * ~~~~~~~~~~~~~~~~~~~ * * UBI volumes are created via the %UBI_IOCMKVOL ioctl command of UBI character * device. A &struct ubi_mkvol_req object has to be properly filled and a * pointer to it has to be passed to the ioctl. * * UBI volume deletion * ~~~~~~~~~~~~~~~~~~~ * * To delete a volume, the %UBI_IOCRMVOL ioctl command of the UBI character * device should be used. A pointer to the 32-bit volume ID hast to be passed * to the ioctl. * * UBI volume re-size * ~~~~~~~~~~~~~~~~~~ * * To re-size a volume, the %UBI_IOCRSVOL ioctl command of the UBI character * device should be used. A &struct ubi_rsvol_req object has to be properly * filled and a pointer to it has to be passed to the ioctl. * * UBI volumes re-name * ~~~~~~~~~~~~~~~~~~~ * * To re-name several volumes atomically at one go, the %UBI_IOCRNVOL command * of the UBI character device should be used. A &struct ubi_rnvol_req object * has to be properly filled and a pointer to it has to be passed to the ioctl. * * UBI volume update * ~~~~~~~~~~~~~~~~~ * * Volume update should be done via the %UBI_IOCVOLUP ioctl command of the * corresponding UBI volume character device. A pointer to a 64-bit update * size should be passed to the ioctl. After this, UBI expects user to write * this number of bytes to the volume character device. The update is finished * when the claimed number of bytes is passed. So, the volume update sequence * is something like: * * fd = open("/dev/my_volume"); * ioctl(fd, UBI_IOCVOLUP, &image_size); * write(fd, buf, image_size); * close(fd); * * Logical eraseblock erase * ~~~~~~~~~~~~~~~~~~~~~~~~ * * To erase a logical eraseblock, the %UBI_IOCEBER ioctl command of the * corresponding UBI volume character device should be used. This command * unmaps the requested logical eraseblock, makes sure the corresponding * physical eraseblock is successfully erased, and returns. * * Atomic logical eraseblock change * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ * * Atomic logical eraseblock change operation is called using the %UBI_IOCEBCH * ioctl command of the corresponding UBI volume character device. A pointer to * a &struct ubi_leb_change_req object has to be passed to the ioctl. Then the * user is expected to write the requested amount of bytes (similarly to what * should be done in case of the "volume update" ioctl). * * Logical eraseblock map * ~~~~~~~~~~~~~~~~~~~~~ * * To map a logical eraseblock to a physical eraseblock, the %UBI_IOCEBMAP * ioctl command should be used. A pointer to a &struct ubi_map_req object is * expected to be passed. The ioctl maps the requested logical eraseblock to * a physical eraseblock and returns. Only non-mapped logical eraseblocks can * be mapped. If the logical eraseblock specified in the request is already * mapped to a physical eraseblock, the ioctl fails and returns error. * * Logical eraseblock unmap * ~~~~~~~~~~~~~~~~~~~~~~~~ * * To unmap a logical eraseblock to a physical eraseblock, the %UBI_IOCEBUNMAP * ioctl command should be used. The ioctl unmaps the logical eraseblocks, * schedules corresponding physical eraseblock for erasure, and returns. Unlike * the "LEB erase" command, it does not wait for the physical eraseblock being * erased. Note, the side effect of this is that if an unclean reboot happens * after the unmap ioctl returns, you may find the LEB mapped again to the same * physical eraseblock after the UBI is run again. * * Check if logical eraseblock is mapped * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ * * To check if a logical eraseblock is mapped to a physical eraseblock, the * %UBI_IOCEBISMAP ioctl command should be used. It returns %0 if the LEB is * not mapped, and %1 if it is mapped. * * Set an UBI volume property * ~~~~~~~~~~~~~~~~~~~~~~~~~ * * To set an UBI volume property the %UBI_IOCSETPROP ioctl command should be * used. A pointer to a &struct ubi_set_vol_prop_req object is expected to be * passed. The object describes which property should be set, and to which value * it should be set. */ /* * When a new UBI volume or UBI device is created, users may either specify the * volume/device number they want to create or to let UBI automatically assign * the number using these constants. */ #define UBI_VOL_NUM_AUTO (-1) #define UBI_DEV_NUM_AUTO (-1) /* Maximum volume name length */ #define UBI_MAX_VOLUME_NAME 127 /* ioctl commands of UBI character devices */ #define UBI_IOC_MAGIC 'o' /* Create an UBI volume */ #define UBI_IOCMKVOL _IOW(UBI_IOC_MAGIC, 0, struct ubi_mkvol_req) /* Remove an UBI volume */ #define UBI_IOCRMVOL _IOW(UBI_IOC_MAGIC, 1, __s32) /* Re-size an UBI volume */ #define UBI_IOCRSVOL _IOW(UBI_IOC_MAGIC, 2, struct ubi_rsvol_req) /* Re-name volumes */ #define UBI_IOCRNVOL _IOW(UBI_IOC_MAGIC, 3, struct ubi_rnvol_req) /* ioctl commands of the UBI control character device */ #define UBI_CTRL_IOC_MAGIC 'o' /* Attach an MTD device */ #define UBI_IOCATT _IOW(UBI_CTRL_IOC_MAGIC, 64, struct ubi_attach_req) /* Detach an MTD device */ #define UBI_IOCDET _IOW(UBI_CTRL_IOC_MAGIC, 65, __s32) /* ioctl commands of UBI volume character devices */ #define UBI_VOL_IOC_MAGIC 'O' /* Start UBI volume update */ #define UBI_IOCVOLUP _IOW(UBI_VOL_IOC_MAGIC, 0, __s64) /* LEB erasure command, used for debugging, disabled by default */ #define UBI_IOCEBER _IOW(UBI_VOL_IOC_MAGIC, 1, __s32) /* Atomic LEB change command */ #define UBI_IOCEBCH _IOW(UBI_VOL_IOC_MAGIC, 2, __s32) /* Map LEB command */ #define UBI_IOCEBMAP _IOW(UBI_VOL_IOC_MAGIC, 3, struct ubi_map_req) /* Unmap LEB command */ #define UBI_IOCEBUNMAP _IOW(UBI_VOL_IOC_MAGIC, 4, __s32) /* Check if LEB is mapped command */ #define UBI_IOCEBISMAP _IOR(UBI_VOL_IOC_MAGIC, 5, __s32) /* Set an UBI volume property */ #define UBI_IOCSETVOLPROP _IOW(UBI_VOL_IOC_MAGIC, 6, \ struct ubi_set_vol_prop_req) /* Maximum MTD device name length supported by UBI */ #define MAX_UBI_MTD_NAME_LEN 127 /* Maximum amount of UBI volumes that can be re-named at one go */ #define UBI_MAX_RNVOL 32 /* * UBI data type hint constants. * * UBI_LONGTERM: long-term data * UBI_SHORTTERM: short-term data * UBI_UNKNOWN: data persistence is unknown * * These constants are used when data is written to UBI volumes in order to * help the UBI wear-leveling unit to find more appropriate physical * eraseblocks. */ enum { UBI_LONGTERM = 1, UBI_SHORTTERM = 2, UBI_UNKNOWN = 3, }; /* * UBI volume type constants. * * @UBI_DYNAMIC_VOLUME: dynamic volume * @UBI_STATIC_VOLUME: static volume */ enum { UBI_DYNAMIC_VOLUME = 3, UBI_STATIC_VOLUME = 4, }; /* * UBI set volume property ioctl constants. * * @UBI_VOL_PROP_DIRECT_WRITE: allow (any non-zero value) or disallow (value 0) * user to directly write and erase individual * eraseblocks on dynamic volumes */ enum { UBI_VOL_PROP_DIRECT_WRITE = 1, }; /** * struct ubi_attach_req - attach MTD device request. * @ubi_num: UBI device number to create * @mtd_num: MTD device number to attach * @vid_hdr_offset: VID header offset (use defaults if %0) * @padding: reserved for future, not used, has to be zeroed * * This data structure is used to specify MTD device UBI has to attach and the * parameters it has to use. The number which should be assigned to the new UBI * device is passed in @ubi_num. UBI may automatically assign the number if * @UBI_DEV_NUM_AUTO is passed. In this case, the device number is returned in * @ubi_num. * * Most applications should pass %0 in @vid_hdr_offset to make UBI use default * offset of the VID header within physical eraseblocks. The default offset is * the next min. I/O unit after the EC header. For example, it will be offset * 512 in case of a 512 bytes page NAND flash with no sub-page support. Or * it will be 512 in case of a 2KiB page NAND flash with 4 512-byte sub-pages. * * But in rare cases, if this optimizes things, the VID header may be placed to * a different offset. For example, the boot-loader might do things faster if * the VID header sits at the end of the first 2KiB NAND page with 4 sub-pages. * As the boot-loader would not normally need to read EC headers (unless it * needs UBI in RW mode), it might be faster to calculate ECC. This is weird * example, but it real-life example. So, in this example, @vid_hdr_offer would * be 2KiB-64 bytes = 1984. Note, that this position is not even 512-bytes * aligned, which is OK, as UBI is clever enough to realize this is 4th * sub-page of the first page and add needed padding. */ struct ubi_attach_req { __s32 ubi_num; __s32 mtd_num; __s32 vid_hdr_offset; __s8 padding[12]; }; /** * struct ubi_mkvol_req - volume description data structure used in * volume creation requests. * @vol_id: volume number * @alignment: volume alignment * @bytes: volume size in bytes * @vol_type: volume type (%UBI_DYNAMIC_VOLUME or %UBI_STATIC_VOLUME) * @padding1: reserved for future, not used, has to be zeroed * @name_len: volume name length * @padding2: reserved for future, not used, has to be zeroed * @name: volume name * * This structure is used by user-space programs when creating new volumes. The * @used_bytes field is only necessary when creating static volumes. * * The @alignment field specifies the required alignment of the volume logical * eraseblock. This means, that the size of logical eraseblocks will be aligned * to this number, i.e., * (UBI device logical eraseblock size) mod (@alignment) = 0. * * To put it differently, the logical eraseblock of this volume may be slightly * shortened in order to make it properly aligned. The alignment has to be * multiple of the flash minimal input/output unit, or %1 to utilize the entire * available space of logical eraseblocks. * * The @alignment field may be useful, for example, when one wants to maintain * a block device on top of an UBI volume. In this case, it is desirable to fit * an integer number of blocks in logical eraseblocks of this UBI volume. With * alignment it is possible to update this volume using plane UBI volume image * BLOBs, without caring about how to properly align them. */ struct ubi_mkvol_req { __s32 vol_id; __s32 alignment; __s64 bytes; __s8 vol_type; __s8 padding1; __s16 name_len; __s8 padding2[4]; char name[UBI_MAX_VOLUME_NAME + 1]; } __packed; /** * struct ubi_rsvol_req - a data structure used in volume re-size requests. * @vol_id: ID of the volume to re-size * @bytes: new size of the volume in bytes * * Re-sizing is possible for both dynamic and static volumes. But while dynamic * volumes may be re-sized arbitrarily, static volumes cannot be made to be * smaller than the number of bytes they bear. To arbitrarily shrink a static * volume, it must be wiped out first (by means of volume update operation with * zero number of bytes). */ struct ubi_rsvol_req { __s64 bytes; __s32 vol_id; } __packed; /** * struct ubi_rnvol_req - volumes re-name request. * @count: count of volumes to re-name * @padding1: reserved for future, not used, has to be zeroed * @vol_id: ID of the volume to re-name * @name_len: name length * @padding2: reserved for future, not used, has to be zeroed * @name: new volume name * * UBI allows to re-name up to %32 volumes at one go. The count of volumes to * re-name is specified in the @count field. The ID of the volumes to re-name * and the new names are specified in the @vol_id and @name fields. * * The UBI volume re-name operation is atomic, which means that should power cut * happen, the volumes will have either old name or new name. So the possible * use-cases of this command is atomic upgrade. Indeed, to upgrade, say, volumes * A and B one may create temporary volumes %A1 and %B1 with the new contents, * then atomically re-name A1->A and B1->B, in which case old %A and %B will * be removed. * * If it is not desirable to remove old A and B, the re-name request has to * contain 4 entries: A1->A, A->A1, B1->B, B->B1, in which case old A1 and B1 * become A and B, and old A and B will become A1 and B1. * * It is also OK to request: A1->A, A1->X, B1->B, B->Y, in which case old A1 * and B1 become A and B, and old A and B become X and Y. * * In other words, in case of re-naming into an existing volume name, the * existing volume is removed, unless it is re-named as well at the same * re-name request. */ struct ubi_rnvol_req { __s32 count; __s8 padding1[12]; struct { __s32 vol_id; __s16 name_len; __s8 padding2[2]; char name[UBI_MAX_VOLUME_NAME + 1]; } ents[UBI_MAX_RNVOL]; } __packed; /** * struct ubi_leb_change_req - a data structure used in atomic LEB change * requests. * @lnum: logical eraseblock number to change * @bytes: how many bytes will be written to the logical eraseblock * @dtype: data type (%UBI_LONGTERM, %UBI_SHORTTERM, %UBI_UNKNOWN) * @padding: reserved for future, not used, has to be zeroed */ struct ubi_leb_change_req { __s32 lnum; __s32 bytes; __s8 dtype; __s8 padding[7]; } __packed; /** * struct ubi_map_req - a data structure used in map LEB requests. * @lnum: logical eraseblock number to unmap * @dtype: data type (%UBI_LONGTERM, %UBI_SHORTTERM, %UBI_UNKNOWN) * @padding: reserved for future, not used, has to be zeroed */ struct ubi_map_req { __s32 lnum; __s8 dtype; __s8 padding[3]; } __packed; /** * struct ubi_set_vol_prop_req - a data structure used to set an UBI volume * property. * @property: property to set (%UBI_VOL_PROP_DIRECT_WRITE) * @padding: reserved for future, not used, has to be zeroed * @value: value to set */ struct ubi_set_vol_prop_req { __u8 property; __u8 padding[7]; __u64 value; } __packed; #endif /* __UBI_USER_H__ */
修改 init/util.c
由於我們增加了一些 ubifs 相關的函式，因此必須自己在 init/util.c 裡面加入相對應的實現。
diff --git a/init/util.c b/init/util.c index 743748b..aa9ca87 100755 --- a/init/util.c +++ b/init/util.c @@ -31,6 +31,8 @@ #include <sys/types.h> #include <sys/socket.h> #include <sys/un.h> +#include <sys/ioctl.h> + /* for ANDROID_SOCKET_* */ #include <cutils/sockets.h> @@ -40,3 +42,4 @@ #include "init.h" #include "log.h" #include "util.h" +#include "ubi-user.h" /* * android_name_to_id - returns the integer uid/gid associated with the given @@ -512,3 +515,99 @@ int restorecon(const char *pathname) #endif return 0; } + +#define UBI_CTRL_DEV "/dev/ubi_ctrl" +#define UBI_SYS_PATH "/sys/class/ubi" + +static int ubi_dev_read_int(int dev, const char *file, int def) +{ + int fd, val = def; + char path[128], buf[64]; + + sprintf(path, UBI_SYS_PATH "/ubi%d/%s", dev, file); + wait_for_file(path, 5); + fd = open(path, O_RDONLY); + if (fd == -1) { + return val; + } + + if (read(fd, buf, 64) > 0) { + val = atoi(buf); + } + + close(fd); + return val; +} + +int ubi_attach_mtd(const char *name) +{ + int ret; + int mtd_num, ubi_num; + int ubi_ctrl, ubi_dev; + int vols, avail_lebs, leb_size; + char path[128]; + struct ubi_attach_req attach_req; + struct ubi_mkvol_req mkvol_req; + + mtd_num = mtd_name_to_number(name); + if (mtd_num == -1) { + return -1; + } + + ubi_ctrl = open(UBI_CTRL_DEV, O_RDONLY); + if (ubi_ctrl == -1) { + return -1; + } + + memset(&attach_req, 0, sizeof(struct ubi_attach_req)); + attach_req.ubi_num = UBI_DEV_NUM_AUTO; + attach_req.mtd_num = mtd_num; + + ret = ioctl(ubi_ctrl, UBI_IOCATT, &attach_req); + if (ret == -1) { + close(ubi_ctrl); + return -1; + } + + ubi_num = attach_req.ubi_num; + + vols = ubi_dev_read_int(ubi_num, "volumes_count", -1); + if (vols == 0) { + sprintf(path, "/dev/ubi%d", ubi_num); + ubi_dev = open(path, O_RDONLY); + if (ubi_dev == -1) { + close(ubi_ctrl); + return ubi_num; + } + + avail_lebs = ubi_dev_read_int(ubi_num, "avail_eraseblocks", 0); + leb_size = ubi_dev_read_int(ubi_num, "eraseblock_size", 0); + + memset(&mkvol_req, 0, sizeof(struct ubi_mkvol_req)); + mkvol_req.vol_id = UBI_VOL_NUM_AUTO; + mkvol_req.alignment = 1; + mkvol_req.bytes = (long long)avail_lebs * leb_size; + mkvol_req.vol_type = UBI_DYNAMIC_VOLUME; + ret = snprintf(mkvol_req.name, UBI_MAX_VOLUME_NAME + 1, "%s", name); + mkvol_req.name_len = ret; + ioctl(ubi_dev, UBI_IOCMKVOL, &mkvol_req); + close(ubi_dev); + } + + close(ubi_ctrl); + return ubi_num; +} + +int ubi_detach_dev(int dev) +{ + int ret, ubi_ctrl; + + ubi_ctrl = open(UBI_CTRL_DEV, O_RDONLY); + if (ubi_ctrl == -1) { + return -1; + } + + ret = ioctl(ubi_ctrl, UBI_IOCDET, &dev); + close(ubi_ctrl); + return ret; +}
ramdisk 修改
將上面的修正加入並重新編譯 Android 後，你就可以在 ramdisk 下使用以下方式去掛載你 的 ubifs 檔案系統，修改 init.*.rc 並添加以下資訊:
mount ubifs ubi@system /system