Hi Sandeep,
Thanks a lot for your reply
On Tue, Jul 21, 2009 at 4:12 PM, SandeepKsinha<sandeepksinha@xxxxxxxxx> wrote:
> Hi Prasad,
>
> On Tue, Jul 21, 2009 at 12:14 PM, Prasad Joshi <prasadjoshi124@xxxxxxxxx>
> wrote:
>>
>> Hi All,
>>
>> I am working on a block device (something similar to the loop device). The
>> block device is associated with a file. So every write or read on block
>> device is intern scheduled to the backing file. Very much similar to the
>> loop device.
>>
>> But, I also need to submit a page full of IOs from the kernel mode. For
>> time being, to make sure it works correctly, I wrote an IOCTL which will
>> create a page, attach buffer heads with it and then call submit_bh(write,
>> bh); to schedule a request to the block device.
>>
>> This is a part of the code
>>
>> int iftl_ioctl (struct block_device *bdev, fmode_t mode, unsigned cmd,
>> unsigned long arg)
>> {
>> struct iftl_device *dev = bdev->bd_disk->private_data;
>> struct buffer_head *bh = NULL, *head = NULL;
>> struct file *file = NULL;
>> int error = 0;
>>
>> ....
>> ....
>>
>> case IFTL_WRITEBLOCK:
>> if (!page) {
>> page = alloc_page(GFP_KERNEL);
>> if (!page) {
>> page = ERR_PTR(-ENOMEM);
>> }
>> if (IS_ERR(page)) {
>> goto ERROR;
>> }
>> }
>>
>> if (!page_has_buffers(page)) {
>> create_empty_buffers(page, PAGE_SIZE, 0);
>> }
>>
>> bh = head = page_buffers(page);
>> fill_data(page);
>>
>> bh->b_blocknr = 0;
>> bh->b_bdev = dev->bdev;
>> bh->b_end_io = end_page_write;
>>
>> set_buffer_locked(bh);
>> set_buffer_mapped(bh);
>>
>> // mark_buffer_dirty(bh);
>>
>> submit_bh(WRITE, bh);
>> break;
>> default:
>> error = -EINVAL;
>> goto ERROR;
>> }
>> ERROR:
>> return error;
>> }
>>
>> But the code fails in generic_make_request() that is called from the
>> submit_bh(). Can someone help?
>
> What exactly does fails or whats the error code that is being returned.
> I suspect playing with some data members of bh. But if you provide the exact
> error ( console logs + dmesg ), it will really be helpful.
Corresponding messages from /var/log/messages file.
Jul 21 01:14:56 anup-laptop kernel: [ 5151.712119] *pde = 00000000
Jul 21 01:14:57 anup-laptop kernel: [ 5151.712119] Modules linked in:
iftl af_packet binfmt_misc sco bridge stp bnep rfcomm l2cap bluetooth
ppdev ipv6 cpufreq_ondemand cpufreq_conservative cpufreq_stats
cpufreq_userspace cpufreq_powersave freq_table sbs video output
processor sbshc container pci_slot iptable_filter ip_tables x_tables
lp snd_intel8x0 snd_ac97_codec ac97_bus snd_pcm_oss snd_mixer_oss
snd_pcm snd_seq_dummy evdev snd_seq_oss snd_seq_midi snd_rawmidi
snd_seq_midi_event parport_pc snd_seq serio_raw psmouse parport
battery ac snd_timer snd_seq_device snd button pcspkr i2c_piix4
soundcore i2c_core snd_page_alloc ext3 jbd mbcache sd_mod crc_t10dif
sr_mod cdrom sg pata_acpi ata_piix ata_generic ohci_hcd ehci_hcd
libata floppy usbcore pcnet32 mii scsi_mod thermal fan fuse [last
unloaded: iftl]
Jul 21 01:14:57 anup-laptop kernel: [ 5151.712119]
Jul 21 01:14:57 anup-laptop kernel: [ 5151.712119] Pid: 5238, comm:
a.out Tainted: G D (2.6.30-rc4 #1) VirtualBox
Jul 21 01:14:57 anup-laptop kernel: [ 5151.712119] EIP:
0060:[<c0252931>] EFLAGS: 00010202 CPU: 0
Jul 21 01:14:57 anup-laptop kernel: [ 5151.712119] EIP is at
generic_make_request+0xa1/0x5b0
Jul 21 01:14:57 anup-laptop kernel: [ 5151.712119] EAX: 00000008 EBX:
d4a6bf00 ECX: 00000000 EDX: 00000575
Jul 21 01:14:57 anup-laptop kernel: [ 5151.712119] ESI: d4a6bf00 EDI:
00000000 EBP: df92fd00 ESP: df92fc28
Jul 21 01:14:57 anup-laptop kernel: [ 5151.712119] DS: 007b ES: 007b
FS: 00d8 GS: 0033 SS: 0069
Jul 21 01:14:57 anup-laptop kernel: [ 5151.712119] 0000080e 00e69000
ff0726f3 0000000a 00000012 00e69000 0000270f 0000270f
Jul 21 01:14:59 anup-laptop kernel: [ 5151.933190] ---[ end trace
e9f702dc2ed6eebd ]---
Instead of filling buffer_heads and passing it to the submit_bh(), I
created the BIO structure passed a page through it. It worked fr me.
Thanks a lot,
Prasad
>
>
>>
>> As the page that I have allocated is not attached with an address_space
>> (mapping) could it be reason for the failure?
>> Do every page used in disk IO needs an associated mapping?
>
> IMO, No.
>
>>
>> Thanks and Regards,
>> Prasad
>
>
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