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diff --git a/Documentation/scsi/st.rst b/Documentation/scsi/st.rst new file mode 100644 index 000000000..d3b28c28d --- /dev/null +++ b/Documentation/scsi/st.rst @@ -0,0 +1,673 @@ +.. SPDX-License-Identifier: GPL-2.0 + +==================== +The SCSI Tape Driver +==================== + +This file contains brief information about the SCSI tape driver. +The driver is currently maintained by Kai Mäkisara (email +Kai.Makisara@kolumbus.fi) + +Last modified: Tue Feb 9 21:54:16 2016 by kai.makisara + + +Basics +====== + +The driver is generic, i.e., it does not contain any code tailored +to any specific tape drive. The tape parameters can be specified with +one of the following three methods: + +1. Each user can specify the tape parameters he/she wants to use +directly with ioctls. This is administratively a very simple and +flexible method and applicable to single-user workstations. However, +in a multiuser environment the next user finds the tape parameters in +state the previous user left them. + +2. The system manager (root) can define default values for some tape +parameters, like block size and density using the MTSETDRVBUFFER ioctl. +These parameters can be programmed to come into effect either when a +new tape is loaded into the drive or if writing begins at the +beginning of the tape. The second method is applicable if the tape +drive performs auto-detection of the tape format well (like some +QIC-drives). The result is that any tape can be read, writing can be +continued using existing format, and the default format is used if +the tape is rewritten from the beginning (or a new tape is written +for the first time). The first method is applicable if the drive +does not perform auto-detection well enough and there is a single +"sensible" mode for the device. An example is a DAT drive that is +used only in variable block mode (I don't know if this is sensible +or not :-). + +The user can override the parameters defined by the system +manager. The changes persist until the defaults again come into +effect. + +3. By default, up to four modes can be defined and selected using the minor +number (bits 5 and 6). The number of modes can be changed by changing +ST_NBR_MODE_BITS in st.h. Mode 0 corresponds to the defaults discussed +above. Additional modes are dormant until they are defined by the +system manager (root). When specification of a new mode is started, +the configuration of mode 0 is used to provide a starting point for +definition of the new mode. + +Using the modes allows the system manager to give the users choices +over some of the buffering parameters not directly accessible to the +users (buffered and asynchronous writes). The modes also allow choices +between formats in multi-tape operations (the explicitly overridden +parameters are reset when a new tape is loaded). + +If more than one mode is used, all modes should contain definitions +for the same set of parameters. + +Many Unices contain internal tables that associate different modes to +supported devices. The Linux SCSI tape driver does not contain such +tables (and will not do that in future). Instead of that, a utility +program can be made that fetches the inquiry data sent by the device, +scans its database, and sets up the modes using the ioctls. Another +alternative is to make a small script that uses mt to set the defaults +tailored to the system. + +The driver supports fixed and variable block size (within buffer +limits). Both the auto-rewind (minor equals device number) and +non-rewind devices (minor is 128 + device number) are implemented. + +In variable block mode, the byte count in write() determines the size +of the physical block on tape. When reading, the drive reads the next +tape block and returns to the user the data if the read() byte count +is at least the block size. Otherwise, error ENOMEM is returned. + +In fixed block mode, the data transfer between the drive and the +driver is in multiples of the block size. The write() byte count must +be a multiple of the block size. This is not required when reading but +may be advisable for portability. + +Support is provided for changing the tape partition and partitioning +of the tape with one or two partitions. By default support for +partitioned tape is disabled for each driver and it can be enabled +with the ioctl MTSETDRVBUFFER. + +By default the driver writes one filemark when the device is closed after +writing and the last operation has been a write. Two filemarks can be +optionally written. In both cases end of data is signified by +returning zero bytes for two consecutive reads. + +Writing filemarks without the immediate bit set in the SCSI command block acts +as a synchronization point, i.e., all remaining data form the drive buffers is +written to tape before the command returns. This makes sure that write errors +are caught at that point, but this takes time. In some applications, several +consecutive files must be written fast. The MTWEOFI operation can be used to +write the filemarks without flushing the drive buffer. Writing filemark at +close() is always flushing the drive buffers. However, if the previous +operation is MTWEOFI, close() does not write a filemark. This can be used if +the program wants to close/open the tape device between files and wants to +skip waiting. + +If rewind, offline, bsf, or seek is done and previous tape operation was +write, a filemark is written before moving tape. + +The compile options are defined in the file linux/drivers/scsi/st_options.h. + +4. If the open option O_NONBLOCK is used, open succeeds even if the +drive is not ready. If O_NONBLOCK is not used, the driver waits for +the drive to become ready. If this does not happen in ST_BLOCK_SECONDS +seconds, open fails with the errno value EIO. With O_NONBLOCK the +device can be opened for writing even if there is a write protected +tape in the drive (commands trying to write something return error if +attempted). + + +Minor Numbers +============= + +The tape driver currently supports up to 2^17 drives if 4 modes for +each drive are used. + +The minor numbers consist of the following bit fields:: + + dev_upper non-rew mode dev-lower + 20 - 8 7 6 5 4 0 + +The non-rewind bit is always bit 7 (the uppermost bit in the lowermost +byte). The bits defining the mode are below the non-rewind bit. The +remaining bits define the tape device number. This numbering is +backward compatible with the numbering used when the minor number was +only 8 bits wide. + + +Sysfs Support +============= + +The driver creates the directory /sys/class/scsi_tape and populates it with +directories corresponding to the existing tape devices. There are autorewind +and non-rewind entries for each mode. The names are stxy and nstxy, where x +is the tape number and y a character corresponding to the mode (none, l, m, +a). For example, the directories for the first tape device are (assuming four +modes): st0 nst0 st0l nst0l st0m nst0m st0a nst0a. + +Each directory contains the entries: default_blksize default_compression +default_density defined dev device driver. The file 'defined' contains 1 +if the mode is defined and zero if not defined. The files 'default_*' contain +the defaults set by the user. The value -1 means the default is not set. The +file 'dev' contains the device numbers corresponding to this device. The links +'device' and 'driver' point to the SCSI device and driver entries. + +Each directory also contains the entry 'options' which shows the currently +enabled driver and mode options. The value in the file is a bit mask where the +bit definitions are the same as those used with MTSETDRVBUFFER in setting the +options. + +A link named 'tape' is made from the SCSI device directory to the class +directory corresponding to the mode 0 auto-rewind device (e.g., st0). + + +Sysfs and Statistics for Tape Devices +===================================== + +The st driver maintains statistics for tape drives inside the sysfs filesystem. +The following method can be used to locate the statistics that are +available (assuming that sysfs is mounted at /sys): + +1. Use opendir(3) on the directory /sys/class/scsi_tape +2. Use readdir(3) to read the directory contents +3. Use regcomp(3)/regexec(3) to match directory entries to the extended + regular expression "^st[0-9]+$" +4. Access the statistics from the /sys/class/scsi_tape/<match>/stats + directory (where <match> is a directory entry from /sys/class/scsi_tape + that matched the extended regular expression) + +The reason for using this approach is that all the character devices +pointing to the same tape drive use the same statistics. That means +that st0 would have the same statistics as nst0. + +The directory contains the following statistics files: + +1. in_flight + - The number of I/Os currently outstanding to this device. +2. io_ns + - The amount of time spent waiting (in nanoseconds) for all I/O + to complete (including read and write). This includes tape movement + commands such as seeking between file or set marks and implicit tape + movement such as when rewind on close tape devices are used. +3. other_cnt + - The number of I/Os issued to the tape drive other than read or + write commands. The time taken to complete these commands uses the + following calculation io_ms-read_ms-write_ms. +4. read_byte_cnt + - The number of bytes read from the tape drive. +5. read_cnt + - The number of read requests issued to the tape drive. +6. read_ns + - The amount of time (in nanoseconds) spent waiting for read + requests to complete. +7. write_byte_cnt + - The number of bytes written to the tape drive. +8. write_cnt + - The number of write requests issued to the tape drive. +9. write_ns + - The amount of time (in nanoseconds) spent waiting for write + requests to complete. +10. resid_cnt + - The number of times during a read or write we found + the residual amount to be non-zero. This should mean that a program + is issuing a read larger thean the block size on tape. For write + not all data made it to tape. + +.. Note:: + + The in_flight value is incremented when an I/O starts the I/O + itself is not added to the statistics until it completes. + +The total of read_cnt, write_cnt, and other_cnt may not total to the same +value as iodone_cnt at the device level. The tape statistics only count +I/O issued via the st module. + +When read the statistics may not be temporally consistent while I/O is in +progress. The individual values are read and written to atomically however +when reading them back via sysfs they may be in the process of being +updated when starting an I/O or when it is completed. + +The value shown in in_flight is incremented before any statstics are +updated and decremented when an I/O completes after updating statistics. +The value of in_flight is 0 when there are no I/Os outstanding that are +issued by the st driver. Tape statistics do not take into account any +I/O performed via the sg device. + +BSD and Sys V Semantics +======================= + +The user can choose between these two behaviours of the tape driver by +defining the value of the symbol ST_SYSV. The semantics differ when a +file being read is closed. The BSD semantics leaves the tape where it +currently is whereas the SYS V semantics moves the tape past the next +filemark unless the filemark has just been crossed. + +The default is BSD semantics. + + +Buffering +========= + +The driver tries to do transfers directly to/from user space. If this +is not possible, a driver buffer allocated at run-time is used. If +direct i/o is not possible for the whole transfer, the driver buffer +is used (i.e., bounce buffers for individual pages are not +used). Direct i/o can be impossible because of several reasons, e.g.: + +- one or more pages are at addresses not reachable by the HBA +- the number of pages in the transfer exceeds the number of + scatter/gather segments permitted by the HBA +- one or more pages can't be locked into memory (should not happen in + any reasonable situation) + +The size of the driver buffers is always at least one tape block. In fixed +block mode, the minimum buffer size is defined (in 1024 byte units) by +ST_FIXED_BUFFER_BLOCKS. With small block size this allows buffering of +several blocks and using one SCSI read or write to transfer all of the +blocks. Buffering of data across write calls in fixed block mode is +allowed if ST_BUFFER_WRITES is non-zero and direct i/o is not used. +Buffer allocation uses chunks of memory having sizes 2^n * (page +size). Because of this the actual buffer size may be larger than the +minimum allowable buffer size. + +NOTE that if direct i/o is used, the small writes are not buffered. This may +cause a surprise when moving from 2.4. There small writes (e.g., tar without +-b option) may have had good throughput but this is not true any more with +2.6. Direct i/o can be turned off to solve this problem but a better solution +is to use bigger write() byte counts (e.g., tar -b 64). + +Asynchronous writing. Writing the buffer contents to the tape is +started and the write call returns immediately. The status is checked +at the next tape operation. Asynchronous writes are not done with +direct i/o and not in fixed block mode. + +Buffered writes and asynchronous writes may in some rare cases cause +problems in multivolume operations if there is not enough space on the +tape after the early-warning mark to flush the driver buffer. + +Read ahead for fixed block mode (ST_READ_AHEAD). Filling the buffer is +attempted even if the user does not want to get all of the data at +this read command. Should be disabled for those drives that don't like +a filemark to truncate a read request or that don't like backspacing. + +Scatter/gather buffers (buffers that consist of chunks non-contiguous +in the physical memory) are used if contiguous buffers can't be +allocated. To support all SCSI adapters (including those not +supporting scatter/gather), buffer allocation is using the following +three kinds of chunks: + +1. The initial segment that is used for all SCSI adapters including + those not supporting scatter/gather. The size of this buffer will be + (PAGE_SIZE << ST_FIRST_ORDER) bytes if the system can give a chunk of + this size (and it is not larger than the buffer size specified by + ST_BUFFER_BLOCKS). If this size is not available, the driver halves + the size and tries again until the size of one page. The default + settings in st_options.h make the driver to try to allocate all of the + buffer as one chunk. +2. The scatter/gather segments to fill the specified buffer size are + allocated so that as many segments as possible are used but the number + of segments does not exceed ST_FIRST_SG. +3. The remaining segments between ST_MAX_SG (or the module parameter + max_sg_segs) and the number of segments used in phases 1 and 2 + are used to extend the buffer at run-time if this is necessary. The + number of scatter/gather segments allowed for the SCSI adapter is not + exceeded if it is smaller than the maximum number of scatter/gather + segments specified. If the maximum number allowed for the SCSI adapter + is smaller than the number of segments used in phases 1 and 2, + extending the buffer will always fail. + + +EOM Behaviour When Writing +========================== + +When the end of medium early warning is encountered, the current write +is finished and the number of bytes is returned. The next write +returns -1 and errno is set to ENOSPC. To enable writing a trailer, +the next write is allowed to proceed and, if successful, the number of +bytes is returned. After this, -1 and the number of bytes are +alternately returned until the physical end of medium (or some other +error) is encountered. + +Module Parameters +================= + +The buffer size, write threshold, and the maximum number of allocated buffers +are configurable when the driver is loaded as a module. The keywords are: + +========================== =========================================== +buffer_kbs=xxx the buffer size for fixed block mode is set + to xxx kilobytes +write_threshold_kbs=xxx the write threshold in kilobytes set to xxx +max_sg_segs=xxx the maximum number of scatter/gather + segments +try_direct_io=x try direct transfer between user buffer and + tape drive if this is non-zero +========================== =========================================== + +Note that if the buffer size is changed but the write threshold is not +set, the write threshold is set to the new buffer size - 2 kB. + + +Boot Time Configuration +======================= + +If the driver is compiled into the kernel, the same parameters can be +also set using, e.g., the LILO command line. The preferred syntax is +to use the same keyword used when loading as module but prepended +with 'st.'. For instance, to set the maximum number of scatter/gather +segments, the parameter 'st.max_sg_segs=xx' should be used (xx is the +number of scatter/gather segments). + +For compatibility, the old syntax from early 2.5 and 2.4 kernel +versions is supported. The same keywords can be used as when loading +the driver as module. If several parameters are set, the keyword-value +pairs are separated with a comma (no spaces allowed). A colon can be +used instead of the equal mark. The definition is prepended by the +string st=. Here is an example:: + + st=buffer_kbs:64,write_threshold_kbs:60 + +The following syntax used by the old kernel versions is also supported:: + + st=aa[,bb[,dd]] + +where: + + - aa is the buffer size for fixed block mode in 1024 byte units + - bb is the write threshold in 1024 byte units + - dd is the maximum number of scatter/gather segments + + +IOCTLs +====== + +The tape is positioned and the drive parameters are set with ioctls +defined in mtio.h The tape control program 'mt' uses these ioctls. Try +to find an mt that supports all of the Linux SCSI tape ioctls and +opens the device for writing if the tape contents will be modified +(look for a package mt-st* from the Linux ftp sites; the GNU mt does +not open for writing for, e.g., erase). + +The supported ioctls are: + +The following use the structure mtop: + +MTFSF + Space forward over count filemarks. Tape positioned after filemark. +MTFSFM + As above but tape positioned before filemark. +MTBSF + Space backward over count filemarks. Tape positioned before + filemark. +MTBSFM + As above but ape positioned after filemark. +MTFSR + Space forward over count records. +MTBSR + Space backward over count records. +MTFSS + Space forward over count setmarks. +MTBSS + Space backward over count setmarks. +MTWEOF + Write count filemarks. +MTWEOFI + Write count filemarks with immediate bit set (i.e., does not + wait until data is on tape) +MTWSM + Write count setmarks. +MTREW + Rewind tape. +MTOFFL + Set device off line (often rewind plus eject). +MTNOP + Do nothing except flush the buffers. +MTRETEN + Re-tension tape. +MTEOM + Space to end of recorded data. +MTERASE + Erase tape. If the argument is zero, the short erase command + is used. The long erase command is used with all other values + of the argument. +MTSEEK + Seek to tape block count. Uses Tandberg-compatible seek (QFA) + for SCSI-1 drives and SCSI-2 seek for SCSI-2 drives. The file and + block numbers in the status are not valid after a seek. +MTSETBLK + Set the drive block size. Setting to zero sets the drive into + variable block mode (if applicable). +MTSETDENSITY + Sets the drive density code to arg. See drive + documentation for available codes. +MTLOCK and MTUNLOCK + Explicitly lock/unlock the tape drive door. +MTLOAD and MTUNLOAD + Explicitly load and unload the tape. If the + command argument x is between MT_ST_HPLOADER_OFFSET + 1 and + MT_ST_HPLOADER_OFFSET + 6, the number x is used sent to the + drive with the command and it selects the tape slot to use of + HP C1553A changer. +MTCOMPRESSION + Sets compressing or uncompressing drive mode using the + SCSI mode page 15. Note that some drives other methods for + control of compression. Some drives (like the Exabytes) use + density codes for compression control. Some drives use another + mode page but this page has not been implemented in the + driver. Some drives without compression capability will accept + any compression mode without error. +MTSETPART + Moves the tape to the partition given by the argument at the + next tape operation. The block at which the tape is positioned + is the block where the tape was previously positioned in the + new active partition unless the next tape operation is + MTSEEK. In this case the tape is moved directly to the block + specified by MTSEEK. MTSETPART is inactive unless + MT_ST_CAN_PARTITIONS set. +MTMKPART + Formats the tape with one partition (argument zero) or two + partitions (argument non-zero). If the argument is positive, + it specifies the size of partition 1 in megabytes. For DDS + drives and several early drives this is the physically first + partition of the tape. If the argument is negative, its absolute + value specifies the size of partition 0 in megabytes. This is + the physically first partition of many later drives, like the + LTO drives from LTO-5 upwards. The drive has to support partitions + with size specified by the initiator. Inactive unless + MT_ST_CAN_PARTITIONS set. +MTSETDRVBUFFER + Is used for several purposes. The command is obtained from count + with mask MT_SET_OPTIONS, the low order bits are used as argument. + This command is only allowed for the superuser (root). The + subcommands are: + + * 0 + The drive buffer option is set to the argument. Zero means + no buffering. + * MT_ST_BOOLEANS + Sets the buffering options. The bits are the new states + (enabled/disabled) the following options (in the + parenthesis is specified whether the option is global or + can be specified differently for each mode): + + MT_ST_BUFFER_WRITES + write buffering (mode) + MT_ST_ASYNC_WRITES + asynchronous writes (mode) + MT_ST_READ_AHEAD + read ahead (mode) + MT_ST_TWO_FM + writing of two filemarks (global) + MT_ST_FAST_EOM + using the SCSI spacing to EOD (global) + MT_ST_AUTO_LOCK + automatic locking of the drive door (global) + MT_ST_DEF_WRITES + the defaults are meant only for writes (mode) + MT_ST_CAN_BSR + backspacing over more than one records can + be used for repositioning the tape (global) + MT_ST_NO_BLKLIMS + the driver does not ask the block limits + from the drive (block size can be changed only to + variable) (global) + MT_ST_CAN_PARTITIONS + enables support for partitioned + tapes (global) + MT_ST_SCSI2LOGICAL + the logical block number is used in + the MTSEEK and MTIOCPOS for SCSI-2 drives instead of + the device dependent address. It is recommended to set + this flag unless there are tapes using the device + dependent (from the old times) (global) + MT_ST_SYSV + sets the SYSV semantics (mode) + MT_ST_NOWAIT + enables immediate mode (i.e., don't wait for + the command to finish) for some commands (e.g., rewind) + MT_ST_NOWAIT_EOF + enables immediate filemark mode (i.e. when + writing a filemark, don't wait for it to complete). Please + see the BASICS note about MTWEOFI with respect to the + possible dangers of writing immediate filemarks. + MT_ST_SILI + enables setting the SILI bit in SCSI commands when + reading in variable block mode to enhance performance when + reading blocks shorter than the byte count; set this only + if you are sure that the drive supports SILI and the HBA + correctly returns transfer residuals + MT_ST_DEBUGGING + debugging (global; debugging must be + compiled into the driver) + + * MT_ST_SETBOOLEANS, MT_ST_CLEARBOOLEANS + Sets or clears the option bits. + * MT_ST_WRITE_THRESHOLD + Sets the write threshold for this device to kilobytes + specified by the lowest bits. + * MT_ST_DEF_BLKSIZE + Defines the default block size set automatically. Value + 0xffffff means that the default is not used any more. + * MT_ST_DEF_DENSITY, MT_ST_DEF_DRVBUFFER + Used to set or clear the density (8 bits), and drive buffer + state (3 bits). If the value is MT_ST_CLEAR_DEFAULT + (0xfffff) the default will not be used any more. Otherwise + the lowermost bits of the value contain the new value of + the parameter. + * MT_ST_DEF_COMPRESSION + The compression default will not be used if the value of + the lowermost byte is 0xff. Otherwise the lowermost bit + contains the new default. If the bits 8-15 are set to a + non-zero number, and this number is not 0xff, the number is + used as the compression algorithm. The value + MT_ST_CLEAR_DEFAULT can be used to clear the compression + default. + * MT_ST_SET_TIMEOUT + Set the normal timeout in seconds for this device. The + default is 900 seconds (15 minutes). The timeout should be + long enough for the retries done by the device while + reading/writing. + * MT_ST_SET_LONG_TIMEOUT + Set the long timeout that is used for operations that are + known to take a long time. The default is 14000 seconds + (3.9 hours). For erase this value is further multiplied by + eight. + * MT_ST_SET_CLN + Set the cleaning request interpretation parameters using + the lowest 24 bits of the argument. The driver can set the + generic status bit GMT_CLN if a cleaning request bit pattern + is found from the extended sense data. Many drives set one or + more bits in the extended sense data when the drive needs + cleaning. The bits are device-dependent. The driver is + given the number of the sense data byte (the lowest eight + bits of the argument; must be >= 18 (values 1 - 17 + reserved) and <= the maximum requested sense data sixe), + a mask to select the relevant bits (the bits 9-16), and the + bit pattern (bits 17-23). If the bit pattern is zero, one + or more bits under the mask indicate cleaning request. If + the pattern is non-zero, the pattern must match the masked + sense data byte. + + (The cleaning bit is set if the additional sense code and + qualifier 00h 17h are seen regardless of the setting of + MT_ST_SET_CLN.) + +The following ioctl uses the structure mtpos: + +MTIOCPOS + Reads the current position from the drive. Uses + Tandberg-compatible QFA for SCSI-1 drives and the SCSI-2 + command for the SCSI-2 drives. + +The following ioctl uses the structure mtget to return the status: + +MTIOCGET + Returns some status information. + The file number and block number within file are returned. The + block is -1 when it can't be determined (e.g., after MTBSF). + The drive type is either MTISSCSI1 or MTISSCSI2. + The number of recovered errors since the previous status call + is stored in the lower word of the field mt_erreg. + The current block size and the density code are stored in the field + mt_dsreg (shifts for the subfields are MT_ST_BLKSIZE_SHIFT and + MT_ST_DENSITY_SHIFT). + The GMT_xxx status bits reflect the drive status. GMT_DR_OPEN + is set if there is no tape in the drive. GMT_EOD means either + end of recorded data or end of tape. GMT_EOT means end of tape. + + +Miscellaneous Compile Options +============================= + +The recovered write errors are considered fatal if ST_RECOVERED_WRITE_FATAL +is defined. + +The maximum number of tape devices is determined by the define +ST_MAX_TAPES. If more tapes are detected at driver initialization, the +maximum is adjusted accordingly. + +Immediate return from tape positioning SCSI commands can be enabled by +defining ST_NOWAIT. If this is defined, the user should take care that +the next tape operation is not started before the previous one has +finished. The drives and SCSI adapters should handle this condition +gracefully, but some drive/adapter combinations are known to hang the +SCSI bus in this case. + +The MTEOM command is by default implemented as spacing over 32767 +filemarks. With this method the file number in the status is +correct. The user can request using direct spacing to EOD by setting +ST_FAST_EOM 1 (or using the MT_ST_OPTIONS ioctl). In this case the file +number will be invalid. + +When using read ahead or buffered writes the position within the file +may not be correct after the file is closed (correct position may +require backspacing over more than one record). The correct position +within file can be obtained if ST_IN_FILE_POS is defined at compile +time or the MT_ST_CAN_BSR bit is set for the drive with an ioctl. +(The driver always backs over a filemark crossed by read ahead if the +user does not request data that far.) + + +Debugging Hints +=============== + +Debugging code is now compiled in by default but debugging is turned off +with the kernel module parameter debug_flag defaulting to 0. Debugging +can still be switched on and off with an ioctl. To enable debug at +module load time add debug_flag=1 to the module load options, the +debugging output is not voluminous. Debugging can also be enabled +and disabled by writing a '0' (disable) or '1' (enable) to the sysfs +file /sys/bus/scsi/drivers/st/debug_flag. + +If the tape seems to hang, I would be very interested to hear where +the driver is waiting. With the command 'ps -l' you can see the state +of the process using the tape. If the state is D, the process is +waiting for something. The field WCHAN tells where the driver is +waiting. If you have the current System.map in the correct place (in +/boot for the procps I use) or have updated /etc/psdatabase (for kmem +ps), ps writes the function name in the WCHAN field. If not, you have +to look up the function from System.map. + +Note also that the timeouts are very long compared to most other +drivers. This means that the Linux driver may appear hung although the +real reason is that the tape firmware has got confused. |