Package com.github.marschall.nativebytebuffers

Class Seals

java.lang.Object
com.github.marschall.nativebytebuffers.Seals
public final class Seals extends Object

  • Field Details

    • F_SEAL_SEAL

      public static final int F_SEAL_SEAL
      If this seal is set, any further call to Fcntl.fcntl(int, int, int) with FcntlCommands.F_ADD_SEALS fails with the error EPERM. Therefore, this seal prevents any modifications to the set of seals itself. If the initial set of seals of a file includes F_SEAL_SEAL, then this effectively causes the set of seals to be constant and locked.
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    • F_SEAL_SHRINK

      public static final int F_SEAL_SHRINK
      If this seal is set, the file in question cannot be reduced in size. This affects open(2) with the O_TRUNC flag as well as truncate(2) and ftruncate(2). Those calls fail with EPERM if you try to shrink the file in question. Increasing the file size is still possible.
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    • F_SEAL_GROW

      public static final int F_SEAL_GROW
      If this seal is set, the size of the file in question cannot be increased. This affects write(2) beyond the end of the file, truncate(2), ftruncate(2), and fallocate(2). These calls fail with EPERM if you use them to increase the file size. If you keep the size or shrink it, those calls still work as expected.
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    • F_SEAL_WRITE

      public static final int F_SEAL_WRITE
      If this seal is set, you cannot modify the contents of the file. Note that shrinking or growing the size of the file is still possible and allowed. Thus, this seal is normally used in combination with one of the other seals. This seal affects write(2) and fallocate(2) (only in combination with the FALLOC_FL_PUNCH_HOLE flag). Those calls fail with EPERM if this seal is set. Furthermore, trying to create new shared, writable memory-mappings via Mman.mmap(int, int, int) will also fail with EPERM.

      Using the FcntlCommands.F_ADD_SEALS operation to set the F_SEAL_WRITE seal fails with EBUSY if any writable, shared mapping exists. Such mappings must be unmapped before you can add this seal. Furthermore, if there are any asynchronous I/O operations (io_submit(2)) pending on the file, all outstanding writes will be discarded.

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    • F_SEAL_FUTURE_WRITE

      public static final int F_SEAL_FUTURE_WRITE
      The effect of this seal is similar to F_SEAL_WRITE, but the contents of the file can still be modified via shared writable mappings that were created prior to the seal being set. Any attempt to create a new writable mapping on the file via Mman.mmap(int, int, int) will fail with EPERM. Likewise, an attempt to write to the file via write(2) will fail with EPERM.

      Using this seal, one process can create a memory buffer that it can continue to modify while sharing that buffer on a "read-only" basis with other processes.

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