December 2011 - kernelnewbies@kernelnewbies.org

PCI device disappeared
by Vimal Dec. 5, 2011

Dec. 5, 2011

A (pointer dereference) bug in my kernel module crashed the system, and when I rebooted, a network PCI device went missing. Several reboots didn't bring back the device, but a cold reboot did! I am curious: what could have caused this issue? -- Vimal

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USB SDCardReader hangs
by Jalil Karimov Dec. 3, 2011

Dec. 3, 2011

Hi All, Here lsusb -v output: Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub Device Descriptor: bLength 18 bDescriptorType 1 bcdUSB 2.00 bDeviceClass 9 Hub bDeviceSubClass 0 Unused bDeviceProtocol 0 Full speed (or root) hub bMaxPacketSize0 64 idVendor 0x1d6b Linux Foundation idProduct 0x0002 2.0 root hub bcdDevice 3.00 iManufacturer 3 Linux 3.0.0-13-generic ehci_hcd iProduct 2 EHCI Host Controller iSerial 1 0000:00:1d.7 bNumConfigurations 1 Configuration Descriptor: bLength 9 bDescriptorType 2 wTotalLength 25 bNumInterfaces 1 bConfigurationValue 1 iConfiguration 0 bmAttributes 0xe0 Self Powered Remote Wakeup MaxPower 0mA Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 0 bAlternateSetting 0 bNumEndpoints 1 bInterfaceClass 9 Hub bInterfaceSubClass 0 Unused bInterfaceProtocol 0 Full speed (or root) hub iInterface 0 Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x81 EP 1 IN bmAttributes 3 Transfer Type Interrupt Synch Type None Usage Type Data wMaxPacketSize 0x0004 1x 4 bytes bInterval 12 Hub Descriptor: bLength 9 bDescriptorType 41 nNbrPorts 6 wHubCharacteristic 0x000a No power switching (usb 1.0) Per-port overcurrent protection bPwrOn2PwrGood 10 * 2 milli seconds bHubContrCurrent 0 milli Ampere DeviceRemovable 0x00 PortPwrCtrlMask 0xff Hub Port Status: Port 1: 0000.0100 power Port 2: 0000.0100 power Port 3: 0000.0100 power Port 4: 0000.0100 power Port 5: 0000.0100 power Port 6: 0000.0100 power Device Status: 0x0003 Self Powered Remote Wakeup Enabled Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub Device Descriptor: bLength 18 bDescriptorType 1 bcdUSB 1.10 bDeviceClass 9 Hub bDeviceSubClass 0 Unused bDeviceProtocol 0 Full speed (or root) hub bMaxPacketSize0 64 idVendor 0x1d6b Linux Foundation idProduct 0x0001 1.1 root hub bcdDevice 3.00 iManufacturer 3 Linux 3.0.0-13-generic uhci_hcd iProduct 2 UHCI Host Controller iSerial 1 0000:00:1d.0 bNumConfigurations 1 Configuration Descriptor: bLength 9 bDescriptorType 2 wTotalLength 25 bNumInterfaces 1 bConfigurationValue 1 iConfiguration 0 bmAttributes 0xe0 Self Powered Remote Wakeup MaxPower 0mA Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 0 bAlternateSetting 0 bNumEndpoints 1 bInterfaceClass 9 Hub bInterfaceSubClass 0 Unused bInterfaceProtocol 0 Full speed (or root) hub iInterface 0 Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x81 EP 1 IN bmAttributes 3 Transfer Type Interrupt Synch Type None Usage Type Data wMaxPacketSize 0x0002 1x 2 bytes bInterval 255 Hub Descriptor: bLength 9 bDescriptorType 41 nNbrPorts 2 wHubCharacteristic 0x000a No power switching (usb 1.0) Per-port overcurrent protection bPwrOn2PwrGood 1 * 2 milli seconds bHubContrCurrent 0 milli Ampere DeviceRemovable 0x00 PortPwrCtrlMask 0xff Hub Port Status: Port 1: 0000.0100 power Port 2: 0000.0100 power Device Status: 0x0003 Self Powered Remote Wakeup Enabled Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub Device Descriptor: bLength 18 bDescriptorType 1 bcdUSB 1.10 bDeviceClass 9 Hub bDeviceSubClass 0 Unused bDeviceProtocol 0 Full speed (or root) hub bMaxPacketSize0 64 idVendor 0x1d6b Linux Foundation idProduct 0x0001 1.1 root hub bcdDevice 3.00 iManufacturer 3 Linux 3.0.0-13-generic uhci_hcd iProduct 2 UHCI Host Controller iSerial 1 0000:00:1d.1 bNumConfigurations 1 Configuration Descriptor: bLength 9 bDescriptorType 2 wTotalLength 25 bNumInterfaces 1 bConfigurationValue 1 iConfiguration 0 bmAttributes 0xe0 Self Powered Remote Wakeup MaxPower 0mA Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 0 bAlternateSetting 0 bNumEndpoints 1 bInterfaceClass 9 Hub bInterfaceSubClass 0 Unused bInterfaceProtocol 0 Full speed (or root) hub iInterface 0 Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x81 EP 1 IN bmAttributes 3 Transfer Type Interrupt Synch Type None Usage Type Data wMaxPacketSize 0x0002 1x 2 bytes bInterval 255 Hub Descriptor: bLength 9 bDescriptorType 41 nNbrPorts 2 wHubCharacteristic 0x000a No power switching (usb 1.0) Per-port overcurrent protection bPwrOn2PwrGood 1 * 2 milli seconds bHubContrCurrent 0 milli Ampere DeviceRemovable 0x00 PortPwrCtrlMask 0xff Hub Port Status: Port 1: 0000.0100 power Port 2: 0000.0100 power Device Status: 0x0003 Self Powered Remote Wakeup Enabled Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub Device Descriptor: bLength 18 bDescriptorType 1 bcdUSB 1.10 bDeviceClass 9 Hub bDeviceSubClass 0 Unused bDeviceProtocol 0 Full speed (or root) hub bMaxPacketSize0 64 idVendor 0x1d6b Linux Foundation idProduct 0x0001 1.1 root hub bcdDevice 3.00 iManufacturer 3 Linux 3.0.0-13-generic uhci_hcd iProduct 2 UHCI Host Controller iSerial 1 0000:00:1d.2 bNumConfigurations 1 Configuration Descriptor: bLength 9 bDescriptorType 2 wTotalLength 25 bNumInterfaces 1 bConfigurationValue 1 iConfiguration 0 bmAttributes 0xe0 Self Powered Remote Wakeup MaxPower 0mA Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 0 bAlternateSetting 0 bNumEndpoints 1 bInterfaceClass 9 Hub bInterfaceSubClass 0 Unused bInterfaceProtocol 0 Full speed (or root) hub iInterface 0 Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x81 EP 1 IN bmAttributes 3 Transfer Type Interrupt Synch Type None Usage Type Data wMaxPacketSize 0x0002 1x 2 bytes bInterval 255 Hub Descriptor: bLength 9 bDescriptorType 41 nNbrPorts 2 wHubCharacteristic 0x000a No power switching (usb 1.0) Per-port overcurrent protection bPwrOn2PwrGood 1 * 2 milli seconds bHubContrCurrent 0 milli Ampere DeviceRemovable 0x00 PortPwrCtrlMask 0xff Hub Port Status: Port 1: 0000.0100 power Port 2: 0000.0103 power enable connect Device Status: 0x0003 Self Powered Remote Wakeup Enabled Bus 004 Device 002: ID 0cf2:6220 ENE Technology, Inc. SD Card Reader (SG361) Device Descriptor: bLength 18 bDescriptorType 1 bcdUSB 1.00 bDeviceClass 0 (Defined at Interface level) bDeviceSubClass 0 bDeviceProtocol 0 bMaxPacketSize0 64 idVendor 0x0cf2 ENE Technology, Inc. idProduct 0x6220 SD Card Reader (SG361) bcdDevice 1.00 iManufacturer 1 ENE iProduct 2 UB6220 iSerial 4 606569746801 bNumConfigurations 1 Configuration Descriptor: bLength 9 bDescriptorType 2 wTotalLength 32 bNumInterfaces 1 bConfigurationValue 1 iConfiguration 0 bmAttributes 0x80 (Bus Powered) MaxPower 498mA Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 0 bAlternateSetting 0 bNumEndpoints 2 bInterfaceClass 8 Mass Storage bInterfaceSubClass 6 SCSI bInterfaceProtocol 80 Bulk (Zip) iInterface 0 Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x01 EP 1 OUT bmAttributes 2 Transfer Type Bulk Synch Type None Usage Type Data wMaxPacketSize 0x0040 1x 64 bytes bInterval 0 Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x82 EP 2 IN bmAttributes 2 Transfer Type Bulk Synch Type None Usage Type Data wMaxPacketSize 0x0040 1x 64 bytes bInterval 0 Device Status: 0x0000 (Bus Powered) * * * Device works fine on OSwintXP and DSL Linux (2.4.31) 52 MB RAM I didn't find 2.4 kernel to build and test myself. After sticking the device's led is blinking and any operations (mount,fdisk,eject) will hang. dmesg outputs (on linux 2.6 and 3.0 same thing) * * * [ 101.868018] usb 1-6: new high speed USB device using ehci_hcd and address 2 [ 101.936241] hub 1-0:1.0: unable to enumerate USB device on port 6 [ 102.204027] usb 4-2: new full speed USB device using uhci_hcd and address 2 [ 102.543218] usbcore: registered new interface driver uas [ 102.583332] Initializing USB Mass Storage driver... [ 102.583535] scsi2 : usb-storage 4-2:1.0 [ 102.585561] usbcore: registered new interface driver usb-storage [ 102.585568] USB Mass Storage support registered. [ 103.596815] scsi 2:0:0:0: Direct-Access USB2.0 CardReader SD 0100 PQ: 0 ANSI: 0 [ 103.603436] sd 2:0:0:0: Attached scsi generic sg3 type 0 [ 103.695769] sd 2:0:0:0: [sdc] 994304 512-byte logical blocks: (509 MB/485 MiB) [ 103.698770] sd 2:0:0:0: [sdc] Write Protect is off [ 103.698778] sd 2:0:0:0: [sdc] Mode Sense: 03 00 00 00 [ 103.698782] sd 2:0:0:0: [sdc] Assuming drive cache: write through [ 103.711757] sd 2:0:0:0: [sdc] Assuming drive cache: write through [ 103.717889] sdc: sdc1 [ 103.727830] sd 2:0:0:0: [sdc] Assuming drive cache: write through [ 103.727841] sd 2:0:0:0: [sdc] Attached SCSI removable disk [ 283.802708] sd 2:0:0:0: timing out command, waited 180s [ 283.802729] sd 2:0:0:0: [sdc] Unhandled sense code [ 283.802733] sd 2:0:0:0: [sdc] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE [ 283.802739] sd 2:0:0:0: [sdc] Sense Key : Hardware Error [current] [ 283.802746] sd 2:0:0:0: [sdc] Add. Sense: Unrecovered read error [ 283.802753] sd 2:0:0:0: [sdc] CDB: Read(10): 28 00 00 0f 2b f0 00 00 08 00 [ 283.802765] end_request: I/O error, dev sdc, sector 994288 [ 283.802773] Buffer I/O error on device sdc, logical block 124286 [ 463.818656] sd 2:0:0:0: timing out command, waited 180s [ 463.818673] sd 2:0:0:0: [sdc] Unhandled sense code [ 463.818677] sd 2:0:0:0: [sdc] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE [ 463.818683] sd 2:0:0:0: [sdc] Sense Key : Hardware Error [current] [ 463.818690] sd 2:0:0:0: [sdc] Add. Sense: Unrecovered read error [ 463.818698] sd 2:0:0:0: [sdc] CDB: Read(10): 28 00 00 0f 2b f0 00 00 08 00 [ 463.818711] end_request: I/O error, dev sdc, sector 994288 [ 463.818719] Buffer I/O error on device sdc1, logical block 124030 [ 480.168080] INFO: task udisks-part-id:1945 blocked for more than 120 seconds. [ 480.168087] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 480.168092] udisks-part-id D 00000000 0 1945 518 0x00000004 [ 480.168100] c0081d9c 00000086 00000000 00000000 ffffffff 00000040 ca73e78c c183a8c0 [ 480.168109] 890837a7 00000050 ca73e788 c183a8c0 c183a8c0 de8068c0 ca73e500 c1731f60 [ 480.168117] 00000246 c1784140 c1784140 00000001 c0081d90 00000246 de25e150 cd208060 [ 480.168126] Call Trace: [ 480.168141] [<c1272d12>] ? kobject_get+0x12/0x20 [ 480.168149] [<c1263888>] ? get_disk+0x48/0xa0 [ 480.168159] [<c1509096>] __mutex_lock_slowpath+0xd6/0x140 [ 480.168164] [<c1508c05>] mutex_lock+0x25/0x40 [ 480.168171] [<c1154e87>] __blkdev_get+0x47/0x360 [ 480.168176] [<c11551e9>] blkdev_get+0x49/0x250 [ 480.168181] [<c11547ae>] ? bd_acquire+0x3e/0xd0 [ 480.168185] [<c1155448>] blkdev_open+0x58/0x70 [ 480.168191] [<c11253c1>] __dentry_open+0xc1/0x280 [ 480.168196] [<c112672e>] nameidata_to_filp+0x6e/0x80 [ 480.168201] [<c11553f0>] ? blkdev_open+0x0/0x70 [ 480.168207] [<c1133bdf>] finish_open+0xaf/0x1a0 [ 480.168211] [<c1133488>] ? do_path_lookup+0x68/0x120 [ 480.168217] [<c1134227>] do_filp_open+0x207/0x6e0 [ 480.168223] [<c1126796>] do_sys_open+0x56/0x120 [ 480.168231] [<c13222d0>] ? write_null+0x0/0x10 [ 480.168236] [<c112688e>] sys_open+0x2e/0x40 [ 480.168241] [<c150a4a4>] syscall_call+0x7/0xb [ 600.168074] INFO: task udisks-daemon:1597 blocked for more than 120 seconds. [ 600.168081] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 600.168085] udisks-daemon D fe1248b5 0 1597 1 0x00000000 [ 600.168093] ca401ca4 00000086 0000006b fe1248b5 0000006b d8e01f16 cd3d9bcc c183a8c0 [ 600.168102] fe126839 0000006b cd3d9bc8 c183a8c0 c183a8c0 de8068c0 cd3d9940 d0eb25e0 [ 600.168110] de806920 de806904 d0eb260c d0eb260c ca401c9c 003d0f91 d90a9ef1 cd3d996c [ 600.168119] Call Trace: [ 600.168137] [<c15088dd>] schedule_timeout+0x1ed/0x260 [ 600.168144] [<c150a07d>] ? _raw_spin_lock+0xd/0x10 [ 600.168152] [<c103de37>] ? task_rq_lock+0x47/0x80 [ 600.168158] [<c1049f53>] ? try_to_wake_up+0x223/0x3c0 [ 600.168164] [<c1508460>] wait_for_common+0xa0/0x130 [ 600.168169] [<c104a124>] ? wake_up_process+0x14/0x20 [ 600.168173] [<c104a0f0>] ? default_wake_function+0x0/0x20 [ 600.168179] [<c15085c7>] wait_for_completion+0x17/0x20 [ 600.168186] [<c1068100>] flush_work+0x30/0x40 [ 600.168192] [<c10666d0>] ? wq_barrier_func+0x0/0x20 [ 600.168197] [<c10697eb>] flush_delayed_work+0x3b/0x40 [ 600.168203] [<c12650a5>] disk_clear_events+0x75/0x120 [ 600.168210] [<c1153c0d>] check_disk_change+0x2d/0x70 [ 600.168218] [<c1362d80>] sd_open+0xa0/0x1d0 [ 600.168224] [<c1272cad>] ? kobject_put+0x1d/0x50 [ 600.168230] [<c1155162>] __blkdev_get+0x322/0x360 [ 600.168236] [<c11551e9>] blkdev_get+0x49/0x250 [ 600.168240] [<c11547ae>] ? bd_acquire+0x3e/0xd0 [ 600.168245] [<c1155448>] blkdev_open+0x58/0x70 [ 600.168251] [<c11253c1>] __dentry_open+0xc1/0x280 [ 600.168256] [<c112672e>] nameidata_to_filp+0x6e/0x80 [ 600.168260] [<c11553f0>] ? blkdev_open+0x0/0x70 [ 600.168266] [<c1133bdf>] finish_open+0xaf/0x1a0 [ 600.168271] [<c1133488>] ? do_path_lookup+0x68/0x120 [ 600.168276] [<c1134227>] do_filp_open+0x207/0x6e0 [ 600.168284] [<c113ff79>] ? vfsmount_lock_local_unlock+0x19/0x20 [ 600.168290] [<c1126796>] do_sys_open+0x56/0x120 [ 600.168295] [<c112859d>] ? fput+0x1d/0x30 [ 600.168299] [<c112688e>] sys_open+0x2e/0x40 [ 600.168305] [<c150a4a4>] syscall_call+0x7/0xb [ 600.168317] INFO: task udisks-part-id:1945 blocked for more than 120 seconds. [ 600.168320] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 600.168324] udisks-part-id D 00000000 0 1945 518 0x00000004 [ 600.168330] c0081d9c 00000086 00000000 00000000 ffffffff 00000040 ca73e78c c183a8c0 [ 600.168338] 890837a7 00000050 ca73e788 c183a8c0 c183a8c0 de8068c0 ca73e500 c1731f60 [ 600.168347] 00000246 c1784140 c1784140 00000001 c0081d90 00000246 de25e150 cd208060 [ 600.168355] Call Trace: [ 600.168361] [<c1272d12>] ? kobject_get+0x12/0x20 [ 600.168368] [<c1263888>] ? get_disk+0x48/0xa0 [ 600.168374] [<c1509096>] __mutex_lock_slowpath+0xd6/0x140 [ 600.168380] [<c1508c05>] mutex_lock+0x25/0x40 [ 600.168385] [<c1154e87>] __blkdev_get+0x47/0x360 [ 600.168390] [<c11551e9>] blkdev_get+0x49/0x250 [ 600.168395] [<c11547ae>] ? bd_acquire+0x3e/0xd0 [ 600.168400] [<c1155448>] blkdev_open+0x58/0x70 [ 600.168404] [<c11253c1>] __dentry_open+0xc1/0x280 [ 600.168409] [<c112672e>] nameidata_to_filp+0x6e/0x80 [ 600.168414] [<c11553f0>] ? blkdev_open+0x0/0x70 [ 600.168419] [<c1133bdf>] finish_open+0xaf/0x1a0 [ 600.168424] [<c1133488>] ? do_path_lookup+0x68/0x120 [ 600.168429] [<c1134227>] do_filp_open+0x207/0x6e0 [ 600.168435] [<c1126796>] do_sys_open+0x56/0x120 [ 600.168442] [<c13222d0>] ? write_null+0x0/0x10 [ 600.168447] [<c112688e>] sys_open+0x2e/0x40 [ 600.168452] [<c150a4a4>] syscall_call+0x7/0xb [ 643.826626] sd 2:0:0:0: timing out command, waited 180s [ 643.826645] sd 2:0:0:0: [sdc] Unhandled sense code [ 643.826649] sd 2:0:0:0: [sdc] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE [ 643.826655] sd 2:0:0:0: [sdc] Sense Key : Hardware Error [current] [ 643.826662] sd 2:0:0:0: [sdc] Add. Sense: Unrecovered read error [ 643.826669] sd 2:0:0:0: [sdc] CDB: Read(10): 28 00 00 0f 2b f0 00 00 08 00 [ 643.826682] end_request: I/O error, dev sdc, sector 994288 [ 643.826690] Buffer I/O error on device sdc1, logical block 124030 Cheers, Jalil

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problem sending INIT_SIPI_SIPI through code
by Vaibhav Jain Dec. 2, 2011

Dec. 2, 2011

Hi, I am trying to execute a c program to send the INIT-SIPI-SIPI sequence to a core after making it go offline (echo 0 > /sys/devices/system/cpu/cpu3/online). But it seems that the program is not working because when it reads back the apic register just after writing to it the value is not the same as what was written.Following is the code for the program. The apic id of the core to be restarted is 5 as seen from cat /proc/cpuinfo. Please let me know if I am doing something wrong. Thanks - Vaibhav Jain * Code : * typedef unsigned int u32; #define MAP_LEN 0x1000 //4 KB page #define BUFLEN 100 #define APIC_BASE 0xfee00000 #define APIC_ICR_low 0xfee00300 #define APIC_ICR_high 0xfee00310 #define APIC_ICR_init 0x00004500 #define APIC_ICR_start 0x00004600 #define BOUNCE_CODE 0x1000 int apic_reset_cpu(cpu); int main() { int cpu; //make sure we have root permissions if(iopl(3)) { printf("Cannot get I/O permissions (being root helps)\n"); return -1; } cpu = 5; if ((apic_reset_cpu(cpu)) != 0) printf("INIT & Startup failed!\n"); printf("INIT / SIPI sequence complete\n"); return 0; } int apic_reset_cpu(int cpu) { unsigned long tmpaddress, apic_icr, *apic_phy_addr; int fd, sleep_now=0; //open the main memory file fd = open ( "/dev/mem", O_RDWR); printf("Assuming APIC physical base: %lx \n", APIC_BASE); tmpaddress = (unsigned long) mmap(NULL, MAP_LEN, PROT_READ|PROT_WRITE, MAP_SHARED, fd, (off_t)APIC_BASE); if(tmpaddress == (unsigned long)MAP_FAILED) //check if it worked { perror("Mapping memory for absolute memory access failed.\n"); return -3; } //prep ICR high apic_icr = tmpaddress; apic_icr +=0x310; apic_phy_addr = (unsigned long *) apic_icr; *apic_phy_addr = cpu << 24; //read the value back printf("\nICR high = %lx\n",*apic_phy_addr); //prep ICR low Send INIT and wait apic_icr = tmpaddress; apic_icr += 0x300; apic_phy_addr = (unsigned long *) apic_icr; *apic_phy_addr = APIC_ICR_init; sleep_now = usleep( 10000 ); //sleep 10 ms printf("\nINIT SENT\n"); //read the value back printf("\nICR low = %lx\n",*apic_phy_addr); //prep ICR high again* apic_icr = tmpaddress; apic_icr +=0x310; apic_phy_addr = (unsigned long *) apic_icr; *apic_phy_addr = cpu << 24; //prep for SIPI apic_icr = tmpaddress; apic_icr += 0x300; apic_phy_addr = (unsigned long *) apic_icr; *apic_phy_addr = APIC_ICR_start | (BOUNCE_CODE >> 12); sleep_now = usleep( 500 ); //sleep 500 usec printf("\nSIPI SENT\n"); //read the value back printf("\nICR low = %lx\n",*apic_phy_addr); *apic_phy_addr = APIC_ICR_start | (BOUNCE_CODE >> 12); printf("\nSIPI SENT AGAIN\n"); //read the value back printf("\nICR low = %lx\n",*apic_phy_addr); printf("Unmapping APIC Base page\n"); tmpaddress &= 0xfffff000; munmap(tmpaddress, MAP_LEN); return 0; }

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contribute to linux kernel
by Mayank Agarwal Dec. 2, 2011

Dec. 2, 2011

Hi all, I have just joined the kernelnewbies.I want to contribute to linux kernel or to any of the open source ongoing projects.Has good experience in c,c++ and linux programming. Please suggest how can i go about that. Regards, Mayank

3 3

What is the purpose of parse_elf() in misc.c
by Graeme Russ Dec. 2, 2011

Dec. 2, 2011

Hi All, In looking at booting a raw x86 kernel image, I discovered that the compressed image in bzImage is actually an ELF image created with: objcopy -R .comment -S vmlinux After decompressing the image, the parse_elf() function in misc.c copies the sections from the ELF image (there are 3 sections, only 2 are marked PT_LOAD) into their final resting place in memory. This got me to thinking, why not use: objcopy -O binary -R .comment -S vmlinux I wrote a little stand-alone parse_elf() program, and lo-and-behold, the outputs are identical. So, in theory, if bzImage contained a raw binary, it could be decompressed directly to the target address. Now there is some adjustment in parse_elf() for relocatable kernels, but I can't but think that this could be simply catered for in the decompression target address Surely this would speed up kernel loading by removing the additional copy that parse_elf() introduces Or am I missing something significant? Regards, Graeme

2 1

Understanding kmap/kunmap
by Kai Meyer Dec. 1, 2011

Dec. 1, 2011

I want to be able to copy data into a struct bio *, so I use bio_for_each_segment to loop through each bvec, like so: void some_function(struct bio *bio, char *some_data) { struct bio_vec *bvec; int i; unsigned int bio_so_far = 0; bio_for_each_segment(bvec, bio, i) { char *bio_buffer = __bio_kmap_atomic(bio, i, KM_USER0); memcpy(bio_buffer, some_data + bio_so_far, bvec->bv_len); __bio_kunmap_atomic(bio, KM_USER0); bio_so_far += bvec->bv_len; } } There's lots more to the function, but this is basically the distilled version with out any extra stuff. What I'm finding is that when the bio has multiple bvecs that share the same page, only the first bvec's data actually gets copied back up to user-space, the rest is garbage or null (meaning, what was there already). For instance, I see a lot of bios from vfat that are 4096 bytes long but are comprised of 8 bvecs that are 512 bytes long that all have an offset to the same page. I've tried doing just one kmap_atomic on the page by keeping track of what the last page I kmap'ed was, but that didn't fix the problem either. Any documentation or high level explanation of kmap/kunmap or other ideas to try are welcome. -Kai Meyer

1 1

modify bootlog in linux
by Mayank Agarwal Dec. 1, 2011

Dec. 1, 2011

Hi, I am trying to learn linux.I have following doubts: 1.In which files/directory we initialize bootlog.which files i have to change in order to modify boot log. how to make a process run as daemon process. 2.Also about linux boot sequence,help/tutorial on linux boot sequence. 3.Major steps in bringing up the new custom evm board. 4.Things to know in order to write the bootloader. Thanks and Regards, Mayank

4 4

About signal handler install info
by naveen yadav Dec. 1, 2011

Dec. 1, 2011

Dear All, I want to know is there any method/API to know whether there is previous signal handler for specific signal no. Example: In below case we install 3 handler. So my question is if before calling signal (SIGUSR1, handler2); is there any way i can get info that there is "handler1" already install with SIGUSR1. signal (SIGUSR1, handler1); signal (SIGUSR1, handler2); signal (SIGUSR1, handler3); #include <stdio.h> #include <stdlib.h> #include <pthread.h> #include <signal.h> void *func (); void handler1 () { printf ("\nIn handler 1\n"); } void handler2 () { printf ("\nIn handler 2\n"); } void handler3 () { printf ("\nIn handler 3\n"); } int main () { int err=-1; pthread_t t1,t2; signal (SIGUSR1, handler1); sleep(5); signal (SIGUSR1, handler2); sleep(5); signal (SIGUSR1, handler3); sleep(5); pthread_create (&t1, NULL, &func, NULL); sleep(20); return 0; } void *func() { while (1) usleep(10); }

2 1