get device flags by device name

Question

hope you can help me: I'm trying to determine whether the device is removable or not, all i have is device name (/dev/sdc). Actually, I need to determine when the file on removable media or on local disk by full path of this file.

I've tryed to search in the current->fs->pwd and all I could find is a set of flags here: *current->fs->pwd.mnt->mnt_sb->s_bdev->bd_disk->flags* where GENHD_FL_REMOVABLE set for removable devices

But i always get the same flags set (as i understand, s_bdev always points to the same device (/dev/sda)).

So now i get the device name (/dev/sdc) that contains my file by parsing mtab, but still can't find out, removable it or not.

Is there possible way to get block_device structure by device name? (for example, "file" structure may be obtained by calling fd = open("name") fl = fged(fd) where fl points to "file" structure)

Infirmity

Answer 1

You can iterate over block devices using class_dev_iter_init and class_dev_iter_next. See the code in block/genhd.c blk_lookup_devt for usage.

Once you have the device, you can use dev_to_disk to get a struct gendisk *, in which you can check the removable flag.

Mcnamara

So, using this way, how I can determine which one of block devices contains my opened file if i have only full path to this file. – Infirmity

@Makc: I think you can use vfs_stat, it will give you a struct kstat in which you will be able to compare the dev_t to the block device. – Mcnamara

I've meet some troubles using class_dev_iter_init and class_dev_iter_next. (system halts on class_dev_iter_next and disk_type is undefined, however his parameter is not necessary.) So, I have found get_gendisk() function that takes dev_t and returns gendisk link, this is what i need, but how can I use this function ? It defined in /include/linux/genhd.h, but including this header makes module compile with warning and insmod fails with Unknown symbol in module. So, is it possible to use this function in kern module ? – Infirmity

@Makc: It appears that get_gendisk() should be exported in recent kernels, was not previously. If recompiling the kernel is an option, either update your kernel, or add a EXPORT_SYMBOL to genhd.c – Mcnamara

Kernel recompiling isn't option. I can't beleave that simple operation, like just obtaining list of block devices can be so complicated or even not possible 0_o. – Infirmity

@Makc: As I said, that was changed in a more recent kernel (though I'm having trouble pinpointing the exact version). I may have found an alternate path though, it's a bit ugly, as in vfs_fstatat get a path via user_path_at, then go through either mnt.mnt_sb or dentry.d_sb to get to your block_device and gendisk – Mcnamara

Finally, this code really works, in some cases I get EFAULT error when calling user_path_at(), but I'll fix it next week and share source that works fine (at least on kernel 2.6.32.33). @Mcnamara , thank you very much. – Infirmity

Answer 2

Read /sys/block/dev-name/removable as it should contain 1 if the device is removable or 0 if not. (dev-name = the device's name: sda, hda, fd0, ...)

Jamal

i know about this, but it's not working under old linux versions, anyway, thank you. – Infirmity

Also, i don't know any safe ways to read files from kernel modules. (I've tryed sys_read() and vfs_read() - it's causes "Oops" :) ) Maybe you know any ways to acces sysfs from kernel module ? – Infirmity