Documentation/userspace-api/unshare.rst

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37 outside the confinement of all-or-nothing shared resources of legacy
45 Al Viro in the August of 2000, on the Linux-Kernel mailing list, as part
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59 even non-threaded applications if they have a need to disassociate
60 from default shared namespace. The following lists two use-cases
63 2.1 Per-security context namespaces
67 the kernel's per-process namespace mechanism. Polyinstantiated directories,
68 such as per-user and/or per-security context instance of /tmp, /var/tmp or
69 per-security context instance of a user's home directory, isolate user
74 of shared-tree feature in the Linux kernel, even regular Linux systems
87 disassociate parts of the context during the servicing of the
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115 allowed incremental context unsharing in future without an ABI change.
118 new context flags without requiring a rebuild of old applications.
119 If and when new context flags are added, unshare() design should allow
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126 	unshare - disassociate parts of the process execution context
135 	context that are currently being shared with other processes. Part
136 	of execution context, such as the namespace, is shared by default
143 	shared execution context without creating a new process.
145 	The flags argument specifies one or bitwise-or'ed of several of
166 	On success, zero returned. On failure, -1 is returned and errno is
169 	EPERM	CLONE_NEWNS was specified by a non-root process (process
173 		context that need to be unshared.
178 	The unshare() call is Linux-specific and  should  not be used
185 --------------------
188 appropriate process context structures, populates it with values from
194   1) clone operates on a newly allocated not-yet-active task
197      before associating newly duplicated context structures
199   2) unshare() has to allocate and duplicate all context structures
212 current context structure was moved into new dup_* functions. Now,
214 appropriate context structures and then associate them with the
220   2) For each context structure, call the corresponding unshare()
221      helper function to allocate and duplicate a new context
225      are new context structures then lock the current task structure,
226      associate new context structures with the current task structure,
229   4) Appropriately release older, shared, context structures.
232 -------------------
241   c) unshare() helper functions for each different process context
254 context structure. The reorganized copy_* functions invoked
268        * For each context flag, invoke the corresponding unshare_*
274 	 modify appropriate context pointers, and release the
284 and CLONE_THREAD, return -EINVAL since they are not implemented yet.
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303      yet, return -EINVAL.
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