Lines Matching full:id
24 we're talking about an id in the upper or lower idmapset.
58 and id ``k11000`` which has been generated by the first idmapping by mapping
62 what id ``k11000`` corresponds to in the second or third idmapping. The
79 an id mapped. We can simply say that ``u1000`` is unmapped in the second and
83 The algorithm to calculate what a given id maps to is pretty simple. First, we
84 need to verify that the range can contain our target id. We will skip this step
85 for simplicity. After that if we want to know what ``id`` maps to we can do
91 id - u + k = n
96 id - k + u = n
108 want to know what id this was mapped from in the upper idmapset of the first
111 id - k + u = n
114 Now assume we are given the id ``u1100`` in the upper idmapset of the second
115 idmapping and we want to know what this id maps down to in the lower idmapset
119 id - u + k = n
128 userspace-id:kernel-id:range
130 A userspace id is always an element in the upper idmapset of an idmapping of
131 type ``uid_t`` or ``gid_t`` and a kernel id is always an element in the lower
133 "userspace id" will be used to refer to the well known ``uid_t`` and ``gid_t``
134 types and "kernel id" will be used to refer to ``kuid_t`` and ``kgid_t``.
138 A userspace id on the other hand is an id that is reported to userspace by the
139 kernel, or is passed by userspace to the kernel, or a raw device id that is
149 For example, within this idmapping, the id ``u1000`` is an id in the upper
151 ``k11000`` which is a kernel id in the lower idmapset or "kernel idmapset"
154 A kernel id is always created by an idmapping. Such idmappings are associated
173 ownership of a file is read from disk by a filesystem, the userspace id is
174 immediately translated into a kernel id according to the idmapping associated
182 simply the identity idmapping. This would mean id ``u1000`` read from disk
183 would be mapped to id ``k1000``. So an inode's ``i_uid`` and ``i_gid`` field
203 If we've been given ``k11000`` from one idmapping we can map that id up in
205 the same kernel id in their kernel idmapsets. For example, consider the
212 then translate ``k11000`` into a userspace id in the second idmapping using the
215 /* Map the kernel id up into a userspace id in the second idmapping. */
218 Note, how we can get back to the kernel id in the first idmapping by inverting
221 /* Map the userspace id down into a kernel id in the second idmapping. */
224 /* Map the kernel id up into a userspace id in the first idmapping. */
227 This algorithm allows us to answer the question what userspace id a given
228 kernel id corresponds to in a given idmapping. In order to be able to answer
229 this question both idmappings need to contain the same kernel id in their
232 For example, when the kernel reads a raw userspace id from disk it maps it down
233 into a kernel id according to the idmapping associated with the filesystem.
240 ownership information about the file the kernel can't simply map the id back up
244 So the kernel will map the id back up in the idmapping of the caller. Let's
252 It is possible to translate a kernel id from one idmapping to another one via
254 a kernel id.
262 kernel id in the first idmapping into a kernel id in the second idmapping we
265 1. Map the kernel id up into a userspace id in the first idmapping::
267 /* Map the kernel id up into a userspace id in the first idmapping. */
270 2. Map the userspace id down into a kernel id in the second idmapping::
272 /* Map the userspace id down into a kernel id in the second idmapping. */
276 the kernel id in one idmapping to a kernel id in another idmapping.
278 This allows us to answer the question what kernel id we would need to use to
279 get the same userspace id in another idmapping. In order to be able to answer
280 this question both idmappings need to contain the same userspace id in their
283 Note, how we can easily get back to the kernel id in the first idmapping by
286 1. Map the kernel id up into a userspace id in the second idmapping::
288 /* Map the kernel id up into a userspace id in the second idmapping. */
291 2. Map the userspace id down into a kernel id in the first idmapping::
293 /* Map the userspace id down into a kernel id in the first idmapping. */
298 userspace id mapped. This will come in handy when working with idmapped mounts.
303 It is never valid to use an id in the kernel idmapset of one idmapping as the
304 id in the userspace idmapset of another or the same idmapping. While the kernel
305 idmapset always indicates an idmapset in the kernel id space the userspace
306 idmapset indicates a userspace id. So the following translations are forbidden::
308 /* Map the userspace id down into a kernel id in the first idmapping. */
311 /* INVALID: Map the kernel id down into a kernel id in the second idmapping. */
317 /* Map the kernel id up into a userspace id in the first idmapping. */
320 /* INVALID: Map the userspace id up into a userspace id in the second idmapping. */
331 The concepts of mapping an id down or mapping an id up are expressed in the two
335 /* Map the userspace id down into a kernel id. */
338 /* Map the kernel id up into a userspace id. */
366 the kernel id back up into a userspace id when writing to disk.
367 So with the second step the kernel guarantees that a valid userspace id can be
373 kernel maps the caller's userspace id down into a kernel id according to the
374 caller's idmapping and then maps that kernel id up according to the
394 caller id: u1000
414 on. Ultimately the userspace id that lands on disk will be ``u1000``.
421 caller id: u1000
435 It's immediately clear that while the caller's userspace id could be
449 caller id: u1000
463 We can see that the translation always succeeds. The userspace id that the
465 the kernel id that was created in the caller's idmapping. This has mainly two
469 userspace id. We could only do this if we were to mount the whole filesystem
491 file id: u1000
498 1. Map the userspace id on disk down into a kernel id in the filesystem's
503 2. Map the kernel id up into a userspace id in the caller's idmapping::
507 The crossmapping algorithm fails in this case because the kernel id in the
508 filesystem idmapping cannot be mapped up to a userspace id in the caller's
517 file id: u1000
524 1. Map the userspace id on disk down into a kernel id in the filesystem's
529 2. Map the kernel id up into a userspace id in the caller's idmapping::
533 Again, the crossmapping algorithm fails in this case because the kernel id in
534 the filesystem idmapping cannot be mapped to a userspace id in the caller's
543 1. Map the userspace id on disk down into a kernel id in the filesystem's
548 2. Map the kernel id up into a userspace id in the caller's idmapping::
569 dir id: u0
570 dir/file1 id: u1000
571 dir/file2 id: u2000
581 dir id: u10000
582 dir/file1 id: u11000
583 dir/file2 id: u12000
592 different login userspace ids. Most users will have ``u1000`` as the login id
594 owned by ``u1000``. At uni or at work they may have another login id such as
706 The ``i_*id_into_vfs*id()`` functions translate filesystem's kernel ids into
709 /* Map the filesystem's kernel id up into a userspace id in the filesystem's idmapping. */
712 /* Map the filesystem's userspace id down ito a VFS id in the mount's idmapping. */
717 The ``mapped_fs*id()`` functions translate the caller's kernel ids into
721 /* Map the caller's VFS id up into a userspace id in the mount's idmapping. */
724 /* Map the mount's userspace id down into a kernel id in the filesystem's idmapping. */
738 Assume a file owned by ``u1000`` is read from disk. The filesystem maps this id
744 kernel id up to a userspace id in the caller's idmapping.
748 id into a VFS id in the mount's idmapping::
751 /* Map the filesystem's kernel id up into a userspace id. */
754 /* Map the filesystem's userspace id down into a VFS id in the mount's idmapping. */
758 VFS id in the mount's idmapping into a userspace id in the caller's
769 mapped to a userspace id in the filesystem's idmapping. Since ``k11000`` can't
774 first call ``mapped_fs*id()`` thereby translating the caller's kernel id into
775 a VFS id according to the mount's idmapping::
778 /* Map the caller's kernel id up into a userspace id in the mount's idmapping. */
781 /* Map the mount's userspace id down into a kernel id in the filesystem's idmapping. */
785 userspace id in the filesystem's idmapping::
802 caller id: u1000
814 2. Translate the caller's VFS id into a kernel id in the filesystem's
818 /* Map the VFS id up into a userspace id in the mount's idmapping. */
821 /* Map the userspace id down into a kernel id in the filesystem's idmapping. */
836 caller id: u1000
847 2. Translate the caller's VFS id into a kernel id in the filesystem's
851 /* Map the VFS id up into a userspace id in the mount's idmapping. */
854 /* Map the userspace id down into a kernel id in the filesystem's idmapping. */
869 file id: u1000
877 1. Map the userspace id on disk down into a kernel id in the filesystem's
882 2. Translate the kernel id into a VFS id in the mount's idmapping::
885 /* Map the kernel id up into a userspace id in the filesystem's idmapping. */
888 /* Map the userspace id down into a VFS id in the mounts's idmapping. */
891 3. Map the VFS id up into a userspace id in the caller's idmapping::
896 Earlier, the caller's kernel id couldn't be crossmapped in the filesystems's
906 file id: u1000
914 1. Map the userspace id on disk down into a kernel id in the filesystem's
919 2. Translate the kernel id into a VFS id in the mount's idmapping::
922 /* Map the kernel id up into a userspace id in the filesystem's idmapping. */
925 /* Map the userspace id down into a VFS id in the mounts's idmapping. */
928 3. Map the VFS id up into a userspace id in the caller's idmapping::
933 Earlier, the file's kernel id couldn't be crossmapped in the filesystems's
959 storage. At home they have id ``u1000`` and all files in their home directory
960 are owned by ``u1000`` whereas at uni or work they have login id ``u1125``.
978 caller id: u1125
987 2. Translate the caller's VFS id into a kernel id in the filesystem's
991 /* Map the VFS id up into a userspace id in the mount's idmapping. */
994 /* Map the userspace id down into a kernel id in the filesystem's idmapping. */
1004 Now let's briefly look at what ownership the caller with id ``u1125`` will see
1009 file id: u1000
1014 1. Map the userspace id on disk down into a kernel id in the filesystem's
1019 2. Translate the kernel id into a VFS id in the mount's idmapping::
1022 /* Map the kernel id up into a userspace id in the filesystem's idmapping. */
1025 /* Map the userspace id down into a VFS id in the mounts's idmapping. */
1028 3. Map the VFS id up into a userspace id in the caller's idmapping::
1034 which is the caller's userspace id on their workstation in our example.
1036 The raw userspace id that is put on disk is ``u1000`` so when the user takes