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Subject[PATCH RFC] Add FAT_IOCTL_GET_VOLUME_ID
Date
From: Mike Lockwood <lockwood@android.com>

This patch, originally from Android kernel, adds vfat directory ioctl command
FAT_IOCTL_GET_VOLUME_ID, with this command we can get the vfat volume ID using
following code:

ioctl(dirfd(dir), FAT_IOCTL_GET_VOLUME_ID, &volume_ID)

This patch is a modified version of the patch by Mike Lockwood, with changes
from Dmitry Pervushin, who noticed the original patch makes some volume IDs
abiguous with error returns: for example, if volume id is 0xFFFFFDAD, that
matches -ENOIOCTLCMD, we get "FFFFFFFF" from the user space.

So add a parameter to ioctl to get the correct volume ID.

Cc: dmitry pervushin <dpervushin@gmail.com>
Cc: Mike Lockwood <lockwood@android.com>
Cc: Colin Cross <ccross@android.com>
Cc: Android Kernel Team <kernel-team@android.com>
Cc: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: John Stultz <john.stultz@linaro.org>

Signed-off-by: Bintian Wang <bintian.wang@linaro.org>
---
fs/fat/dir.c | 14 ++++++++++++++
fs/fat/fat.h | 1 +
fs/fat/inode.c | 9 +++++++++
include/uapi/linux/msdos_fs.h | 13 +++++++++++++
4 files changed, 37 insertions(+)

diff --git a/fs/fat/dir.c b/fs/fat/dir.c
index 7a6f02c..4c59108 100644
--- a/fs/fat/dir.c
+++ b/fs/fat/dir.c
@@ -776,12 +776,19 @@ static int fat_ioctl_readdir(struct inode *inode, struct file *filp,
return ret;
}

+static unsigned int fat_ioctl_volume_id(struct inode *inode)
+{
+ struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
+ return sbi->vol_id;
+}
+
static long fat_dir_ioctl(struct file *filp, unsigned int cmd,
unsigned long arg)
{
struct inode *inode = file_inode(filp);
struct __fat_dirent __user *d1 = (struct __fat_dirent __user *)arg;
int short_only, both;
+ unsigned int id;

switch (cmd) {
case VFAT_IOCTL_READDIR_SHORT:
@@ -792,6 +799,9 @@ static long fat_dir_ioctl(struct file *filp, unsigned int cmd,
short_only = 0;
both = 1;
break;
+ case FAT_IOCTL_GET_VOLUME_ID:
+ id = fat_ioctl_volume_id(inode);
+ return copy_to_user((unsigned int *)arg, &id, sizeof(id));
default:
return fat_generic_ioctl(filp, cmd, arg);
}
@@ -822,6 +832,7 @@ static long fat_compat_dir_ioctl(struct file *filp, unsigned cmd,
struct inode *inode = file_inode(filp);
struct compat_dirent __user *d1 = compat_ptr(arg);
int short_only, both;
+ unsigned int id;

switch (cmd) {
case VFAT_IOCTL_READDIR_SHORT32:
@@ -832,6 +843,9 @@ static long fat_compat_dir_ioctl(struct file *filp, unsigned cmd,
short_only = 0;
both = 1;
break;
+ case FAT_IOCTL_GET_VOLUME_ID:
+ id = fat_ioctl_volume_id(inode);
+ return copy_to_user((unsigned int *)arg, &id, sizeof(id));
default:
return fat_generic_ioctl(filp, cmd, (unsigned long)arg);
}
diff --git a/fs/fat/fat.h b/fs/fat/fat.h
index 21664fc..4241e6f 100644
--- a/fs/fat/fat.h
+++ b/fs/fat/fat.h
@@ -86,6 +86,7 @@ struct msdos_sb_info {
const void *dir_ops; /* Opaque; default directory operations */
int dir_per_block; /* dir entries per block */
int dir_per_block_bits; /* log2(dir_per_block) */
+ unsigned int vol_id; /*volume ID*/

int fatent_shift;
struct fatent_operations *fatent_ops;
diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 5d4513c..a14dd4c 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -1252,6 +1252,7 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat,
struct inode *fsinfo_inode = NULL;
struct buffer_head *bh;
struct fat_boot_sector *b;
+ struct fat_boot_bsx *bsx;
struct msdos_sb_info *sbi;
u16 logical_sector_size;
u32 total_sectors, total_clusters, fat_clusters, rootdir_sectors;
@@ -1398,6 +1399,8 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat,
goto out_fail;
}

+ bsx = (struct fat_boot_bsx *)(bh->b_data + FAT32_BSX_OFFSET);
+
fsinfo = (struct fat_boot_fsinfo *)fsinfo_bh->b_data;
if (!IS_FSINFO(fsinfo)) {
fat_msg(sb, KERN_WARNING, "Invalid FSINFO signature: "
@@ -1413,8 +1416,14 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat,
}

brelse(fsinfo_bh);
+ } else {
+ bsx = (struct fat_boot_bsx *)(bh->b_data + FAT16_BSX_OFFSET);
}

+ /* interpret volume ID as a little endian 32 bit integer */
+ sbi->vol_id = (((u32)bsx->vol_id[0]) | ((u32)bsx->vol_id[1] << 8) |
+ ((u32)bsx->vol_id[2] << 16) | ((u32)bsx->vol_id[3] << 24));
+
sbi->dir_per_block = sb->s_blocksize / sizeof(struct msdos_dir_entry);
sbi->dir_per_block_bits = ffs(sbi->dir_per_block) - 1;

diff --git a/include/uapi/linux/msdos_fs.h b/include/uapi/linux/msdos_fs.h
index f055e58..be142ee 100644
--- a/include/uapi/linux/msdos_fs.h
+++ b/include/uapi/linux/msdos_fs.h
@@ -104,6 +104,8 @@ struct __fat_dirent {
/* <linux/videotext.h> has used 0x72 ('r') in collision, so skip a few */
#define FAT_IOCTL_GET_ATTRIBUTES _IOR('r', 0x10, __u32)
#define FAT_IOCTL_SET_ATTRIBUTES _IOW('r', 0x11, __u32)
+/*Android kernel has used 0x12, so we use 0x13*/
+#define FAT_IOCTL_GET_VOLUME_ID _IOR('r', 0x13, __u32)

struct fat_boot_sector {
__u8 ignored[3]; /* Boot strap short or near jump */
@@ -161,6 +163,17 @@ struct fat_boot_fsinfo {
__le32 reserved2[4];
};

+struct fat_boot_bsx {
+ __u8 drive; /* drive number */
+ __u8 reserved1;
+ __u8 signature; /* extended boot signature */
+ __u8 vol_id[4]; /* volume ID */
+ __u8 vol_label[11]; /* volume label */
+ __u8 type[8]; /* file system type */
+};
+#define FAT16_BSX_OFFSET 36 /* offset of fat_boot_bsx in FAT12 and FAT16 */
+#define FAT32_BSX_OFFSET 64 /* offset of fat_boot_bsx in FAT32 */
+
struct msdos_dir_entry {
__u8 name[MSDOS_NAME];/* name and extension */
__u8 attr; /* attribute bits */
--
1.7.9.5


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