sg: max_scatter_elem_sz parameter; lk 2.6.17-rc1
Subsystems (2)
PATCH 1/1 sg: max_scatter_elem_sz parameter; lk 2.6.17-rc1
There is a small band of folks out there who push the "big data transfer per command" limit. That became a more interesting exercise in lk 2.6.16 as discussed in:
http://www.torque.net/sg/sg_io.html [in the maximum transfer size section].
To make the sg driver more flexible in this area, the attachment introduces the max_scatter_elem_sz sysfs/kernel_or_module load time parameter that overrides the SG_SCATTER_SZ define when given.
Post lk 2.6.16 the largest scatter gather element size is limited to MAX_SEGMENT_SIZE [64 KB] unless that is overridden by a blk_queue_max_segment_size() in the LLD.
Changelog:
- add max_scatter_elem_sz parameter; can be read or written in sysfs, or supplied as a kernel load time, or module load time parameter
- bump sg version number to 3.5.34 to reflect change (addition) to its interface
Doug Gilbert
drivers/scsi/sg.c2616max_scat renamed from drivers/scsi/sg.c +10 -4
@@ -18,8 +18,8 @@ * */ -static int sg_version_num = 30533; /* 2 digits for each component */ -#define SG_VERSION_STR "3.5.33" +static int sg_version_num = 30534; /* 2 digits for each component */ +#define SG_VERSION_STR "3.5.34" /* * D. P. Gilbert ([email protected], [email protected]), notes:
@@ -62,7 +62,7 @@ #ifdef CONFIG_SCSI_PROC_FS #include <linux/proc_fs.h> -static char *sg_version_date = "20050908"; +static char *sg_version_date = "20060329"; static int sg_proc_init(void); static void sg_proc_cleanup(void);
@@ -96,6 +96,8 @@ static int def_reserved_size = -1; /* picks up init parameter */ static int sg_allow_dio = SG_ALLOW_DIO_DEF; +static int max_scatter_elem_sz = SG_SCATTER_SZ; + #define SG_SECTOR_SZ 512 #define SG_SECTOR_MSK (SG_SECTOR_SZ - 1)
@@ -1570,6 +1572,7 @@ * of sysfs parameters (which module_param doesn't yet support). * Sysfs parameters defined explicitly below. */ +module_param_named(max_scatter_elem_sz, max_scatter_elem_sz, int, S_IRUGO | S_IWUSR); module_param_named(def_reserved_size, def_reserved_size, int, S_IRUGO); module_param_named(allow_dio, sg_allow_dio, int, S_IRUGO | S_IWUSR);
@@ -1578,6 +1581,8 @@ MODULE_LICENSE("GPL"); MODULE_VERSION(SG_VERSION_STR); +MODULE_PARM_DESC(max_scatter_elem_sz, "maximum scatter gather element " + "size (default: 32768)"); MODULE_PARM_DESC(def_reserved_size, "size of buffer reserved for each fd"); MODULE_PARM_DESC(allow_dio, "allow direct I/O (default: 0 (disallow))");
@@ -1872,7 +1877,8 @@ (rem_sz > 0) && (k < mx_sc_elems); ++k, rem_sz -= ret_sz, ++sg) { - num = (rem_sz > SG_SCATTER_SZ) ? SG_SCATTER_SZ : rem_sz; + num = (rem_sz > max_scatter_elem_sz) ? + max_scatter_elem_sz : rem_sz; p = sg_page_malloc(num, sfp->low_dma, &ret_sz); if (!p) return -ENOMEM;