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memfd_create() is similar to mmap(MAP_ANON), but returns a file-descriptor that you can pass to mmap(). It can support sealing and avoids any connection to user-visible mount-points. Thus, it's not subject to quotas on mounted file-systems, but can be used like malloc()'ed memory, but with a file-descriptor to it. memfd_create() returns the raw shmem file, so calls like ftruncate() can be used to modify the underlying inode. Also calls like fstat() will return proper information and mark the file as regular file. If you want sealing, you can specify MFD_ALLOW_SEALING. Otherwise, sealing is not supported (like on all other regular files). Compared to O_TMPFILE, it does not require a tmpfs mount-point and is not subject to a filesystem size limit. It is still properly accounted to memcg limits, though, and to the same overcommit or no-overcommit accounting as all user memory. Signed-off-by: David Herrmann <[email protected]> Acked-by: Hugh Dickins <[email protected]> Cc: Michael Kerrisk <[email protected]> Cc: Ryan Lortie <[email protected]> Cc: Lennart Poettering <[email protected]> Cc: Daniel Mack <[email protected]> Cc: Andy Lutomirski <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
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#ifndef _UAPI_LINUX_MEMFD_H | ||
#define _UAPI_LINUX_MEMFD_H | ||
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/* flags for memfd_create(2) (unsigned int) */ | ||
#define MFD_CLOEXEC 0x0001U | ||
#define MFD_ALLOW_SEALING 0x0002U | ||
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#endif /* _UAPI_LINUX_MEMFD_H */ |
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