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mount FS without filesystem type
by piyush moghe July 22, 2011

July 22, 2011

I have a question regarding mounting filesystem without giving filesystem type as argument to mount command: AFAIK when mount command is run to mount a FS the corresponding call made in kernel is "compat_sys_mount" as per kernel 2.6.36. Now compat_sys_kernel expects a filesystem "type" name as argument but in compat_sys_mount there is no check for "type" argument as NULL, now as part of this mount path do_kern_mount also called which uses the "type" argument to compat_sys_mount and finds out the corresponding file_system_type structure from the file_system_type structure list and if not matching structure is found it returns with error. 842 asmlinkage long compat_sys_mount(const char __user * dev_name, 843 const char __user * dir_name, 844 const char __user * type, unsigned long flags, <====== type argument to compat_sys_mount 845 const void __user * data) 846 { 847 char *kernel_type; 848 unsigned long data_page; 849 char *kernel_dev; 850 char *dir_page; 851 int retval; 852 853 retval = copy_mount_string(type, &kernel_type); 1098 do_kern_mount(const char *fstype, int flags, const char *name, void *data) 1099 { 1100 struct file_system_type *type = get_fs_type(fstype); <======= same type argument to search in list 1101 struct vfsmount *mnt; 1102 if (!type) <======= if the type name entry not found in list return ERRROR 1103 return ERR_PTR(-ENODEV); 1104 mnt = vfs_kern_mount(type, flags, name, data); 1105 if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) && 1106 !mnt->mnt_sb->s_subtype) 1107 mnt = fs_set_subtype(mnt, fstype); 1108 put_filesystem(type); 1109 return mnt; 1110 } Now my question is that if I don't provide FS type name to mount command how the FS gets mounted. Is there some other path for this code or if before calling compat_sys_mount i.e in user mode FS type is determined somehow? Regards, Piyush

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Problem installing vanilla kernel on Fedora 13
by srivatsa bhat July 22, 2011

July 22, 2011

Hi Vaibhav, >Hi, >I am trying to install an extra vanilla kernel on Fedora 13. The Fedora 13 runs on vmware virtual machine. >I installed it using and iso of live cd. A 'uname -r' gives the version as 2.6.33-85.fc13.i686. >The kernel version I am trying to install is 2.6.38.8 >I am following these steps : >- Download kernel source and unzip it >- make menuconfig (Saved the config) >- make >- make modules_install >- make install >However as soon as i do a 'make install ' an error message appears saying : >"ERROR:modinfo:could not find module i2c_core" >I could find the options for i2c in the config menu and enabled some of them but didn't help. >Could anyone please tell me how to debug this error ? I have tried the same thing on Fedora 14 earlier and there was >no such problem. >Thanks >Vaibhav Jain Try running make localmodconfig after running make menuconfig. The former command finds out all the currently loaded kernel modules, device drivers etc and ensures that all the config options necessary for them are set in the .config file. Regards, Srivatsa S. Bhat

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How to generate PAUSE frame
by bill July 22, 2011

July 22, 2011

Hi, all I have a 10G NIC card with fiber interface, this NIC is drived by a private os with l2 rxonly forwarding function, and I want to test this NIC could sent out PAUSE frame. host client +--------+ +------------+ | | fiber | 10G NIC | | NIC | <===> | l2fwd | | | | rxonly | +--------+ +------------+ If host send packet faster than client could receive, client 10G NIC should send out PAUSE frame, and use "ethtool -a eth0" on host to show any PAUSE frame received. How could I do this without any faster NIC card than 10G? thanks bill

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How to submit multiple related patches
by Zac Storer July 22, 2011

July 22, 2011

What is the best way to send multiple related patches? for example: A series of patches that fix indentation issues within a single src file.

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How to write portable device drivers?
by gmane＠reliableembeddedsystems.com July 21, 2011

July 21, 2011

Hi, Please correct me, if I'm wrong, but that's my understanding. include/linux/byteorder/generic.h defines macros, which take both the CPU endianess and the endianess of the peripherial device you want to access into account. e.g. cpu_to_le32 will no matter what's the endianess of the CPU write to a little endian 32 address (do the swapping or not) but there are also in lib/iomap.c macros like iowrite32, which don't seem to take the CPU endianess into account Now looking e.g. at drivers/net/e100.c both kind of macros are used. e.g. ioread32 and also cpu_to_le32 The iowritexxx macros seem to boil down to outxx macros and it looks like iomap needs to be called before - maybe the endianess of the CPU is taken into account there, if so it's not obvious to me;) I'm a bit confused since we seem to have I/O ports and I/O memory. Can you please elaborate a bit when to use what and what happens with the CPU endianess in case of ioread/write macros? My goal is to understand how to write portable drivers which can be used with all kinds of funny CPU / peripheral endianess combinations. Regards, Robert ..."Everything should be built top-down, except the first time." My public pgp key is available at: http://pgp.mit.edu:11371/pks/lookup?op=get&search=0x90320BF1

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Regarding remap_pfn_page
by mindentropy July 21, 2011

July 21, 2011

Hi, When I mmap pages via remap_pfn_page method would the physical frames assigned the linear address be contiguous? If yes what would happen if I mmap a huge range? Thanks.

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PCI Driver not writing to Config Space
by Giriprasad Deviprasad July 20, 2011

July 20, 2011

Hi All, I have a pci driver like: define VENDOR_ID 0x1415 #define DEVICE_ID1 0xc140 #include<linux/module.h> #include<linux/version.h> #include<linux/kernel.h> #include<linux/pci.h> #include<linux/ioport.h> #include<asm/unistd.h> #include<linux/slab.h> #include<linux/fs.h> #include<asm/uaccess.h> #include<asm/io.h> #include<linux/kdev_t.h> #include<asm/fcntl.h> #include<linux/sched.h> #include<linux/wait.h> #include<linux/errno.h> #include<asm/irq.h> #include<asm/ioctl.h> #include<linux/string.h> #include<linux/interrupt.h> init_module (void) { short int curr_device; dev = pci_find_device (VENDOR_ID, DEVICE_ID1, NULL); j = pci_enable_device (dev); curr_device = 0; printk("Init : Reading and writing Config space.........\n"); pci_read_config_word (dev, 0x02, (u16 *)&curr_device); printk("Init : Current Device id = %x\n", (curr_device & 0x00FFFF)); curr_device = 0xc145; pci_write_config_word (dev, 0x02, curr_device); pci_read_config_word (dev, 0x02, (u16 *)&curr_device); printk("Init : After writing to Config space, Current Device id = %x\n", (curr_device & 0x00FFFF)); return 0; } void cleanup_module (void) { printk ("Closing pci \n"); } When I insmod this driver after build, it shows: Jul 20 15:11:03 localhost kernel: Init : Reading and writing Config space......... Jul 20 15:11:03 localhost kernel: Init : Current Device id = c140 Jul 20 15:11:03 localhost kernel: Init : After writing to Config space, Current Device id = c140 Any clues as to why is not writing 0xc145 to the pci config space? curr_device = 0xc145; pci_write_config_word (dev, 0x02, curr_device); Thanks & Regards, D.Giriprasad

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why backtiks for a word?
by zeal July 19, 2011

July 19, 2011

Hi list, We often see that `a word what you like'. But i get confused on it. Why is it `word' but not 'word' or what else? -- Cheers - zeal

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Need help understanding memory models, cpu modes and address translation
by Vaibhav Jain July 17, 2011

July 17, 2011

Hi, I am eager to understand the basics of Memory models (flat, segmented etc) , CPU modes (real,protected) and address translation (physical to logical etc.) and how all of them work together. I am very confused about this and would really appreciate if someone could provide good references to these topics. Thanks Vaibhav Jain

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interview question how does application connects to device
by Bond July 17, 2011

July 17, 2011

This is an interview question. I had written device driver for a char device so I know that code structure looks like this struct file_operations something { .owner=my_device_open; .read=my_device_read; .close=my_device_close; .write=my_device_write; } When the device driver is active then in /dev/mydevice you can actually read and write into it. But what I was not clear is how an application will read or write to this device. I know insmod will insert the module to kernel,and register_chrdev(); will register the driver in kernel but how will application program communicate with this driver. My answer was In unix it simply opens the device node as a file and sends/receives data and commands from it. But he was expecting some thing more complex.

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