Messages in this thread | | | From | "Richard W.M. Jones" <> | Subject | [PATCH v4 0/3] vfs: Define new syscall umask2 [formerly getumask] | Date | Wed, 13 Apr 2016 20:05:33 +0100 |
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v3 -> v4:
- Rename the syscall: getumask becomes umask2.
- Add flags parameter, with one flag (UMASK_GET_MASK).
- Expand the rationale for this change in the first commit message.
- Add a selftest.
- Retest everything.
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It's not possible to read the process umask without also modifying it, which is what umask(2) does. A library cannot read umask safely, especially if the main program might be multithreaded.
This patch series adds a new system call "umask2". This adds a flags parameter. Specifying flags=UMASK_GET_MASK allows the umask of the current process to be read without modifying it.
This leaves open the possibility in future of adding a per-thread umask, set or read with other flags. This is not implemented.
Another approach to this has been attempted before, adding something to /proc, although it didn't go anywhere. See:
http://comments.gmane.org/gmane.linux.kernel/1292109
Another way to solve this would be to add a thread-safe getumask to glibc. Since glibc could own the mutex, this would permit libraries linked to this glibc to read umask safely. I should also note that man-pages documents getumask(3), but no version of glibc has ever implemented it.
Rich.
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