patch-2.2.10 linux/include/scsi/sg.h

• Lines: 273
• Date: Mon Jun 7 16:27:06 1999
• Orig file: v2.2.9/linux/include/scsi/sg.h
• Orig date: Tue May 11 13:10:32 1999

diff -u --recursive --new-file v2.2.9/linux/include/scsi/sg.h linux/include/scsi/sg.h
@@ -12,10 +12,16 @@
 *       Copyright (C) 1998, 1999 Douglas Gilbert
 
 
-    Version: 2.1.32 (990501)
-    This version for later 2.1.x series and 2.2.x kernels
+    Version: 2.1.34 (990603)
+    This version for later 2.1.x and 2.2.x series kernels
     D. P. Gilbert (dgilbert@interlog.com, dougg@triode.net.au)
 
+    Changes since 2.1.33 (990521)
+        - implement SG_SET_RESERVED_SIZE and associated memory re-org.
+        - add SG_NEXT_CMD_LEN to override SCSI command lengths
+        - add SG_GET_VERSION_NUM to get version expressed as an integer
+    Changes since 2.1.32 (990501)
+        - fix race condition in sg_read() and sg_open()
     Changes since 2.1.31 (990327)
         - add ioctls SG_GET_UNDERRUN_FLAG and _SET_. Change the default
           to _not_ flag underruns (affects aic7xxx driver)
@@ -25,24 +31,6 @@
     Changes since 2.1.30 (990320)
         - memory tweaks: change flags on kmalloc (GFP_KERNEL to GFP_ATOMIC)
         -                increase max allowable mid-level pool usage
-    Changes since 2.1.21 (990315)
-        - skipped to 2.1.30 indicating interface change (revert to 2.1.9)
-        - remove attempt to accomodate cdrecord 1.8, will fix app
-        - keep SG_?ET_RESERVED_SIZE naming for clarity
-    Changes since 2.1.20 (990313)
-        - ommission: left out logic for SG_?ET_ALT_INTERFACE, now added
-    Changes since 2.1.9 (990309)
-        - skipped to version 2.1.20 to indicate some interface changes
-        - incorporate sg changes to make cdrecord 1.8 work (had its
-          own patches that were different from the original)
-        - change SG_?ET_BUFF_SIZE to SG_?ET_RESERVED_SIZE for clarity
-    Changes since 2.1.8 (990303)
-        - debug ">9" option dumps debug for _all_ active sg devices
-        - increase allowable dma pool usage + increase minimum threshhold
-        - pad out sg_scsi_id structure
-    Changes since 2.1.7 (990227)
-        - command queuing now "non-default" [back. compat. with cdparanoia]
-        - Tighten access on some ioctls
 
 
     New features and changes:
@@ -52,24 +40,32 @@
         - the SCSI target, host and driver status are returned
           in unused fields of sg_header (maintaining its original size).
         - asynchronous notification support added (SIGPOLL, SIGIO) for
-          read()s ( write()s should never block).
-        - pack_id logic added so read() can be made to wait for a specific
-          pack_id. 
+          read()s (write()s should never block).
+        - pack_id logic added so read() can wait for a specific pack_id. 
         - uses memory > ISA_DMA_THRESHOLD if adapter allows it (e.g. a
           pci scsi adapter).
         - this driver no longer uses a single SG_BIG_BUFF sized buffer
-          obtained at driver/module init time. Rather it obtains a 
-          SG_SCATTER_SZ buffer when a fd is open()ed and frees it at
-          the corresponding release() (ie pr fd). Hence open() can return
-          ENOMEM! If write() request > SG_SCATTER_SZ bytes for data then
-          it can fail with ENOMEM as well (if so, scale back).
+          obtained at driver/module init time. Rather it tries to obtain a 
+          SG_DEF_RESERVED_SIZE buffer when a fd is open()ed and frees it
+          at the corresponding release() (ie per fd). Actually the "buffer"
+          may be a collection of buffers if scatter-gather is being used.
+        - add SG_SET_RESERVED_SIZE ioctl allowing the user to request a
+          large buffer for duration of current file descriptor's lifetime.
+        - SG_GET_RESERVED_SIZE ioctl can be used to find out how much
+          actually has been reserved.
+        - add SG_NEXT_CMD_LEN ioctl to override SCSI command length on
+          the next write() to this file descriptor.
+        - SG_GET_RESERVED_SIZE's presence as a symbol can be used for
+          compile time identification of the version 2 sg driver.
+          However, it is recommended that run time identification based on
+          calling the ioctl of the same name is a more flexible and
+          safer approach.
         - adds several ioctl calls, see ioctl section below.
-        - SG_SCATTER_SZ's presence indicates this version of "sg" driver.
  
  Good documentation on the original "sg" device interface and usage can be
- found in the Linux HOWTO document: "SCSI Programming HOWTO" by Heiko
- Eissfeldt; last updated 7 May 1996. I will add more info on using the
- extensions in this driver as required. A quick summary:
+ found in the Linux HOWTO document: "SCSI Programming HOWTO" (version 0.5)
+ by Heiko Eissfeldt; last updated 7 May 1996. Here is a quick summary of
+ sg basics:
  An SG device is accessed by writing SCSI commands plus any associated 
  outgoing data to it; the resulting status codes and any incoming data
  are then obtained by a read call. The device can be opened O_NONBLOCK
@@ -88,38 +84,37 @@
  The given SCSI command has its LUN field overwritten internally by the
  value associated with the device that has been opened.
 
- Memory (RAM) is used within this driver for direct memory access (DMA)
- in transferring data to and from the SCSI device. The dreaded ENOMEM
- seems to be more prevalent under early 2.2.x kernels than under the
- 2.0.x kernel series. For a given (large) transfer the memory obtained by
- this driver must be contiguous or scatter-gather must be used (if
- supported by the adapter). [Furthermore, ISA SCSI adapters can only use
- memory below the 16MB level on a i386.]
- This driver tries hard to find some suitable memory before admitting
- defeat and returning ENOMEM. All is not lost if application writers
- then back off the amount they are requesting. The value returned by
- the SG_GET_RESERVED_SIZE ioctl is guaranteed to be available (one
- per fd). This driver does the following:
-   -  attempts to reserve a SG_SCATTER_SZ sized buffer on open(). The
-      actual amount reserved is given by the SG_GET_RESERVED_SIZE ioctl().
-   -  each write() needs to reserve a DMA buffer of the size of the
-      data buffer indicated (excluding sg_header and command overhead).
-      This buffer, depending on its size, adapter type (ISA or not) and
-      the amount of memory available will be obtained from the kernel
-      directly (get_free_pages or kmalloc) or the from the scsi mid-level
-      dma pool (taking care not to exhaust it).
-      If the buffer requested is > SG_SCATTER_SZ or memory is tight then
-      scatter-gather will be used if supported by the adapter.
-  -   write() will also attempt to use the buffer reserved on open()
-      if it is large enough.
- The above strategy ensures that a write() can always depend on a buffer 
- of the size indicated by the SG_GET_RESERVED_SIZE ioctl() (which could be
- 0, but at least the app knows things are tight in advance).
- Hence application writers can adopt quite aggressive strategies (e.g. 
- requesting 512KB) and scale them back in the face of ENOMEM errors.
- N.B. Queuing up commands also ties up kernel memory.
+ This device currently uses "indirect IO" in the sense that data is
+ DMAed into kernel buffers from the hardware and afterwards is
+ transferred into the user space (or vice versa if you are writing).
+ Transfer speeds or up to 20 to 30MBytes/sec have been measured using
+ indirect IO. For faster throughputs "direct IO" which cuts out the
+ double handling of data is required. This will also need a new interface.
+
+ Grabbing memory for those kernel buffers used in this driver for DMA may
+ cause the dreaded ENOMEM error. This error seems to be more prevalent 
+ under early 2.2.x kernels than under the 2.0.x kernel series. For a given 
+ (large) transfer the memory obtained by this driver must be contiguous or
+ scatter-gather must be used (if supported by the adapter). [Furthermore, 
+ ISA SCSI adapters can only use memory below the 16MB level on a i386.]
+
+ When a "sg" device is open()ed O_RDWR then this driver will attempt to
+ reserve a buffer of SG_DEF_RESERVED_SIZE that will be used by subsequent
+ write()s on this file descriptor as long as:
+    -  it is not already in use (eg when command queuing is in use)
+    -  the write() does not call for a buffer size larger than the
+       reserved size.
+ In these cases the write() will attempt to find the memory it needs for
+ DMA buffers dynamically and in the worst case will fail with ENOMEM.
+ The amount of memory actually reserved depends on various dynamic factors
+ and can be checked with the SG_GET_RESERVED_SIZE ioctl(). [In a very
+ tight memory situation it may yield 0!] The size of the reserved buffer
+ can be changed with the SG_SET_RESERVED_SIZE ioctl(). It should be
+ followed with a call to the SG_GET_RESERVED_SIZE ioctl() to find out how
+ much was actually reserved.
 
- More documentation can be found at www.torque.net/sg
+ More documentation plus test and utility programs can be found at 
+ http://www.torque.net/sg
 */
 
 #define SG_MAX_SENSE 16   /* too little, unlikely to change in 2.2.x */
@@ -129,7 +124,7 @@
     int pack_len;    /* [o] reply_len (ie useless), ignored as input */
     int reply_len;   /* [i] max length of expected reply (inc. sg_header) */
     int pack_id;     /* [io] id number of packet (use ints >= 0) */
-    int result;      /* [o] 0==ok, else (+ve) Unix errno code (e.g. EIO) */
+    int result;      /* [o] 0==ok, else (+ve) Unix errno (best ignored) */
     unsigned int twelve_byte:1; 
         /* [i] Force 12 byte command length for group 6 & 7 commands  */
     unsigned int target_status:5;   /* [o] scsi status from target */
@@ -154,9 +149,9 @@
     int unused3;  
 } Sg_scsi_id;
 
-/* ioctls  ( _GET_s yield result via 'int *' 3rd argument unless 
-            otherwise indicated */
-#define SG_SET_TIMEOUT 0x2201  /* unit: jiffies, 10ms on i386 */
+/* IOCTLs: ( _GET_s yield result via 'int *' 3rd argument unless 
+             otherwise indicated) */
+#define SG_SET_TIMEOUT 0x2201  /* unit: jiffies (10ms on i386) */
 #define SG_GET_TIMEOUT 0x2202  /* yield timeout as _return_ value */
 
 #define SG_EMULATED_HOST 0x2203 /* true for emulated host adapter (ATAPI) */
@@ -165,23 +160,21 @@
 #define SG_SET_TRANSFORM 0x2204
 #define SG_GET_TRANSFORM 0x2205
 
-#define SG_SET_RESERVED_SIZE 0x2275  /* currently ignored, future addition */
-/* Following yields buffer reserved by open(): 0 <= x <= SG_SCATTER_SZ */
-#define SG_GET_RESERVED_SIZE 0x2272
+#define SG_SET_RESERVED_SIZE 0x2275  /* request a new reserved buffer size */
+#define SG_GET_RESERVED_SIZE 0x2272  /* actual size of reserved buffer */
 
 /* The following ioctl takes a 'Sg_scsi_id *' object as its 3rd argument. */
-#define SG_GET_SCSI_ID 0x2276   /* Yields fd's bus,chan,dev,lun+type */
+#define SG_GET_SCSI_ID 0x2276   /* Yields fd's bus, chan, dev, lun + type */
 /* SCSI id information can also be obtained from SCSI_IOCTL_GET_IDLUN */
 
-/* Override adapter setting and always DMA using low memory ( <16MB on i386).
-   Default is 0 (off - use adapter setting) */
+/* Override host setting and always DMA using low memory ( <16MB on i386) */
 #define SG_SET_FORCE_LOW_DMA 0x2279  /* 0-> use adapter setting, 1-> force */
 #define SG_GET_LOW_DMA 0x227a   /* 0-> use all ram for dma; 1-> low dma ram */
 
 /* When SG_SET_FORCE_PACK_ID set to 1, pack_id is input to read() which
    will attempt to read that pack_id or block (or return EAGAIN). If 
    pack_id is -1 then read oldest waiting. When ...FORCE_PACK_ID set to 0
-   (default) then pack_id ignored by read() and oldest readable fetched. */ 
+   then pack_id ignored by read() and oldest readable fetched. */ 
 #define SG_SET_FORCE_PACK_ID 0x227b
 #define SG_GET_PACK_ID 0x227c /* Yields oldest readable pack_id (or -1) */
 
@@ -194,43 +187,47 @@
 /* Yields max scatter gather tablesize allowed by current host adapter */
 #define SG_GET_SG_TABLESIZE 0x227F  /* 0 implies can't do scatter gather */
 
-/* Control whether sequencing per file descriptor (default) or per device */
-#define SG_GET_MERGE_FD 0x2274   /* 0-> per fd (default), 1-> per device */
+/* Control whether sequencing per file descriptor or per device */
+#define SG_GET_MERGE_FD 0x2274   /* 0-> per fd, 1-> per device */
 #define SG_SET_MERGE_FD 0x2273   /* Attempt to change sequencing state,
-  if more than 1 fd open on device, will fail with EBUSY */
+  if more than current fd open on device, will fail with EBUSY */
 
 /* Get/set command queuing state per fd (default is SG_DEF_COMMAND_Q) */
 #define SG_GET_COMMAND_Q 0x2270   /* Yields 0 (queuing off) or 1 (on) */
 #define SG_SET_COMMAND_Q 0x2271   /* Change queuing state with 0 or 1 */
 
-/* Get/set whether DMA underrun will cause an error (DID_ERROR) [this only
-   currently applies to the [much-used] aic7xxx driver) */
+/* Get/set whether DMA underrun will cause an error (DID_ERROR). This only
+   currently applies to the [much-used] aic7xxx driver. */
 #define SG_GET_UNDERRUN_FLAG 0x2280 /* Yields 0 (don't flag) or 1 (flag) */
 #define SG_SET_UNDERRUN_FLAG 0x2281 /* Change flag underrun state */
 
+#define SG_GET_VERSION_NUM 0x2282 /* Example: version 2.1.34 yields 20134 */
+#define SG_NEXT_CMD_LEN 0x2283  /* override SCSI command length with given
+                   number on the next write() on this file descriptor */
+
+
+#define SG_SCATTER_SZ (8 * 4096)  /* PAGE_SIZE not available to user */
+/* Largest size (in bytes) a single scatter-gather list element can have.
+   The value must be a power of 2 and <= (PAGE_SIZE * 32) [131072 bytes on 
+   i386]. The minimum value is PAGE_SIZE. If scatter-gather not supported
+   by adapter then this value is the largest data block that can be
+   read/written by a single scsi command. The user can find the value of
+   PAGE_SIZE by calling getpagesize() defined in unistd.h . */
 
 #define SG_DEFAULT_TIMEOUT (60*HZ) /* HZ == 'jiffies in 1 second' */
 #define SG_DEFAULT_RETRIES 1
 
-/* Default modes, commented if they differ from original sg driver */
+/* Defaults, commented if they differ from original sg driver */
 #define SG_DEF_COMMAND_Q 0
 #define SG_DEF_MERGE_FD 0       /* was 1 -> per device sequencing */
 #define SG_DEF_FORCE_LOW_DMA 0  /* was 1 -> memory below 16MB on i386 */
 #define SG_DEF_FORCE_PACK_ID 0
 #define SG_DEF_UNDERRUN_FLAG 0
+#define SG_DEF_RESERVED_SIZE SG_SCATTER_SZ
 
 /* maximum outstanding requests, write() yields EDOM if exceeded */
 #define SG_MAX_QUEUE 16
 
-#define SG_SCATTER_SZ (8 * 4096)  /* PAGE_SIZE not available to user */
-/* Largest size (in bytes) a single scatter-gather list element can have.
-   The value must be a power of 2 and <= (PAGE_SIZE * 32) [131072 bytes on 
-   i386]. The minimum value is PAGE_SIZE. If scatter-gather not supported
-   by adapter then this value is the largest data block that can be
-   read/written by a single scsi command. Max number of scatter-gather
-   list elements seems to be limited to 255. */
-
-#define SG_BIG_BUFF SG_SCATTER_SZ       /* for backward compatibility */
-/* #define SG_BIG_BUFF (SG_SCATTER_SZ * 8) */ /* =256KB, if you want */
+#define SG_BIG_BUFF SG_DEF_RESERVED_SIZE    /* for backward compatibility */
 
 #endif