Limitations note created

Author: rgmacedo

notes/limitations.md

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+# Current Limitations in the System
+
+### Relative *vs.* Absolute Paths
+For path-based operations, such as `open`, `rename`, `getxattr`, ..., the system only considers the absolute path.
+This is because PADLL needs to check if the path belongs to the targeted mountpoint.
+For example, if the path is `/mnt/data/file.txt` and the target mountpoint is `/mnt`, it will be considered as a valid path;
+however, if the path is `file.txt`, it will be considered as an invalid path.
+
+This has repercussions not only for the path-based operations, but also for those that are dependent on the returned file descriptor.
+
+
+### Close for unregisted file descriptors
+One of the microbenchmarks is to replay the trace of the `close` system call in the ABCI supercomputer.
+However, if the trace replayer only submits "dumb" `close`operations (*i.e.,* random file descriptors), the operation will not be successfully enforced, since at some point in the internal operation flow, it will generate an invalid `workflow identifier` (`static_cast<uint32_t> (-1)`).
+
+
+### File descriptor based operations when `open` is not handled
+If the `open` system call is not handled in the system (`libc_calls::open = false`), then all file descriptor based operations such as `read`, `write`, `close`, ... will not be enforced, since the `MountPointEntry` is not registered.
+