diff options
Diffstat (limited to 'sgm_dd.8')
| -rw-r--r-- | sgm_dd.8 | 24 |
1 files changed, 21 insertions, 3 deletions
@@ -1,4 +1,4 @@ -.TH SGM_DD "8" "January 2007" "sg3_utils\-1.23" SG3_UTILS +.TH SGM_DD "8" "March 2007" "sg3_utils\-1.24" SG3_UTILS .SH NAME sgm_dd \- copies data to and from files and devices. Specialized for devices that understand the SCSI command set and does memory mapped @@ -21,8 +21,16 @@ transfers on sg devices. Similar syntax and semantics to but does not perform any conversions. .PP Will only perform memory mapped transfers when \fIIFILE\fR or \fIOFILE\fR -are SCSI generic (sg) devices. If both \fIIFILE\fR and \fIOFILE\fR are -sg devices then memory mapped transfers are only performed on \fIIFILE\fR. +are SCSI generic (sg) devices. +.PP +If both \fIIFILE\fR and \fIOFILE\fR are sg devices then memory mapped +transfers are performed on \fIIFILE\fR. If no other flags are specified +then indirect IO is performed on \fIOFILE\fR. If 'oflag=dio' is given then +direct IO is attempted on \fIOFILE\fR. If 'oflag=smmap' is given then +shared mmap-ed IO (sharing the mmap-ed reserve buffer associated with +\fIIFILE\fR) is attempted. In both latter cases if the faster IO option +is not available, they fall back to indirect IO and report this at +the end of the copy. .PP The first group in the synopsis above are "standard" Unix .B dd(1) @@ -73,6 +81,7 @@ Only allowed when the read\-side (i.e. \fIIFILE\fR) is a sg device. When 1 there may be a "zero copy" copy (i.e. mmap\-ed transfer on the read into the user space and direct IO from there on the write, potentially two DMAs and no data copying from the CPU). Default is 0. +The same action as 'dio=1' is also available with 'oflag=dio'. .TP \fBibs\fR=\fIBS\fR if given must be the same as \fIBS\fR given to 'bs=' option. @@ -145,6 +154,10 @@ from the beginning of the file or, if \fISEEK\fR is given, starting at block \fISEEK\fR. Note that attempting to 'append' to a device file (e.g. a disk) will usually be ignored or may cause an error to be reported. .TP +dio +is only active with oflag (i.e. 'oflag=dio'). Its action is described in +the 'dio=1' option description above. +.TP direct causes the O_DIRECT flag to be added to the open of \fIIFILE\fR and/or \fIOFILE\fR. This flag requires some memory alignment on IO. Hence user @@ -173,6 +186,11 @@ causes the FUA (force unit access) bit to be set in SCSI READ and/or WRITE commands. This only has effect with sg devices. The 6 byte variants of the SCSI READ and WRITE commands do not support the FUA bit. Only active for sg device file names. +.TP +smmap +is only active for oflag. It sets shared mmap IO usage on \fIOFILE\fR if +it is a sg device node. The \fIIFILE\fR also needs to be a sg device +node (or there is no mmap-ed reserve buffer to share). .SH RETIRED OPTIONS Here are some retired options that are still present: .TP |