cbb2063e__SG_IO_ioctl_in_the_2_6_series_inimum_permission_requirements_Comments
[SCSI command] PREVENT ALLOW MEDIUM REMOVAL [(draft) standard] SPC-4, MMC-4 [sg driver requires] O_RDWR O_RDWR [Comments] 
sd, st and cdrom drivers use this internally
Linux SG_IO ioctl in the 2.6 series
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