following through the code that creates the entire /sys hierarchy and ran across a puzzler involving /sys/block. here are the top-level entries in /sys: $ ls block bus class dev devices firmware fs kernel module power $ and it's easy to use a "grep" to see where most of them come from, assuming most of them are represented by a global variable name ending in "_kobj" as they often do: $ grep -r "_kobj = kobject_create_and_add.*NULL" * arch/powerpc/platforms/pseries/power.c: power_kobj = kobject_create_and_add("power", NULL); drivers/base/hypervisor.c: hypervisor_kobj = kobject_create_and_add("hypervisor", NULL); drivers/base/core.c: dev_kobj = kobject_create_and_add("dev", NULL); drivers/base/firmware.c: firmware_kobj = kobject_create_and_add("firmware", NULL); drivers/staging/speakup/kobjects.c: accessibility_kobj = kobject_create_and_add("accessibility", NULL); fs/namespace.c: fs_kobj = kobject_create_and_add("fs", NULL); kernel/ksysfs.c: kernel_kobj = kobject_create_and_add("kernel", NULL); kernel/power/main.c: power_kobj = kobject_create_and_add("power", NULL); $ but i didn't see the creation of /sys/block and, after a bit of looking, noticed it had a different name -- block_depr -- which doesn't look like it's used all that much: $ grep -rw block_depr * block/genhd.c:struct kobject *block_depr; block/genhd.c: err = sysfs_create_link(block_depr, &ddev->kobj, block/genhd.c: sysfs_remove_link(block_depr, dev_name(disk_to_dev(disk))); block/genhd.c: block_depr = kobject_create_and_add("block", NULL); include/linux/genhd.h:extern struct kobject *block_depr; $ now, given that that kobject is clearly "deprecated", it seemed that it should be configurable to not create it at all and, sure enough, there's what looks like the Kconfig entry in init/Kconfig: config SYSFS_DEPRECATED bool "Enable deprecated sysfs features to support old userspace tools" depends on SYSFS default n help This option adds code that switches the layout of the "block" class devices, to not show up in /sys/class/block/, but only in /sys/block/. ... but that looks a bit strange ... it doesn't omit the creation of /sys/block; rather, it omits the creation of /sys/class/block, which appears to be the *newer* location for that information. and there's this from drivers/base/core.c: ===== start ===== #ifdef CONFIG_SYSFS_DEPRECATED #ifdef CONFIG_SYSFS_DEPRECATED_V2 long sysfs_deprecated = 1; #else long sysfs_deprecated = 0; #endif static __init int sysfs_deprecated_setup(char *arg) { return strict_strtol(arg, 10, &sysfs_deprecated); } early_param("sysfs.deprecated", sysfs_deprecated_setup); #endif ===== end ===== anyway, i explicitly selected no SYSFS_DEPRECATED config settings in my build, but i still got the /sys/block entry under /sys. is it really necessary? if it's "deprecated", should one not be able to configure and build a kernel without it, if the newer(?) location for it is /sys/class/block? thoughts? rday -- ======================================================================== Robert P. J. Day Ottawa, Ontario, CANADA http://crashcourse.ca Twitter: http://twitter.com/rpjday LinkedIn: http://ca.linkedin.com/in/rpjday ========================================================================