Hierarchical file system and anti-tearing algorithm for a limited-resource computer such as a smart card

A hierarchical file system for a limited-resource computer, comprising:

• a directory having an index that uniquely identifies said directory;
• and
• a file having an index that uniquely identifies said directory;
• said directory and said file in combination defining a double-linked set of objects;
• said directory comprising a header memory block that includes an “Up” field that identifies said file as the last object of said double-linked set of objects;
• said file having a header memory block that includes a “Left” field that backward links said file to said header memory block of said directory.

A file of a hierarchical file system of objects for a limited-resource computer system, comprising:

• a header memory block uniquely identified by an index, said header memory block including a header segment and a data segment, said header segment including
• a “Left” field that points to the next object in the hierarchical file system;
• and
• a “Right” field that points to a previous object in the hierarchical file system.

An anti-tearing algorithm for a hierarchical file system of objects of a limited-resource computer system comprising a set of instructions for performing an atomic write operation with respect to any data-protected object of the hierarchical file system while concomitantly ensuring the consistency of data in the data-protected object, said set of instructions including

• an instruction to identify all memory blocks of said data-protected object that are the subject of the atomic write operation;
• an instruction to allocate a number of memory blocks equal to the number of memory blocks of said data-protected object identified as the subject of the atomic write operation;
• an instruction to prepare the allocated memory blocks;
• an instruction to set the backward pointer of the first allocated memory block to the previous memory block of said data-protected object that is unaffected by the atomic write operation;
• an instruction to set the forward pointer of the last allocated memory block to the next memory block of said data-protected object that is unaffected by the atomic write operation;
• an instruction to set the read-direction status bit and the write-in-progress status bit of said data-protected object to one;
• an instruction to set the forward pointer of the previous memory block to point to the first allocated memory block;
• an instruction to clear the read-direction status bit of said data-protected object;
• an instruction to set the backward pointer of the next memory block to the last allocated memory block;
• and
• an instruction to clear the write-in-progress status bit of said data-protected object.

An anti-tearing algorithm for a hierarchical file system of objects of a limited-resource computer system comprising a set of instructions for verifying the consistency of each data-protected object of the hierarchical file system during initialization of the limited-resource computer system by detecting whether any data-protected object was subjected to a write-operation interruption, said set of instructions being further operative, with respect to any data-protected file subjected to a write-operation interruption, to cause the data in such data-protected file to be in the state it was in before the write operation was interrupted or in the state it would be in after the write operation was fully executed, said instructions including

• an instruction to sequentially check the read-direction and write-in-progress status bits of each data-protected object in the hierarchical file system during initialization of the limited-resource computer system;
• an instruction to determine whether the read-direction status bit of the checked data-protected object is set;
• an instruction, if the read-direction status bit of the checked data-protected object is set, to use the correct backward pointers of the data-protected object to fix the forward pointers of the data-protected object as required so that the data-protected object is recovered to its state prior to the atomic write operation;
• an instruction, if the read-direction status bit of the checked data-protected object is not set, to determine whether the write-in-progress status bit of the checked data-protected object is set;
• an instruction, if the write-in-progress status bit of the checked data-protected object is set, to use the correct forward pointers of the data-protected object to fix the backward pointers of the data-protected object as required so that the data-protected object is recovered to its state after full execution of the atomic write operation;
• an instruction, if the write-in-progress status bit of the checked data-protected object is not set, to check the next data-protected file in the hierarchical file system;
• and
• an instruction to repeat the foregoing set of instructions with respect to the next data-protected object in the hierarchical file system until all data-protected object in the hierarchical file system have been completed.

A method for performing an atomic write operation with respect to any data-protected object of a hierarchical file system while concomitantly ensuring the consistency of data in the data-protected object, comprising the steps of:

• identifying all memory blocks of said data-protected object that are the subject of the atomic write operation;
• allocating a number of memory blocks equal to the number of memory blocks of said data-protected object identified as the subject of the atomic write operation;
• preparing the allocated memory blocks;
• setting the backward pointer of the first allocated memory block to the previous memory block of said data-protected object that is unaffected by the atomic write operation;
• setting the forward pointer of the last allocated memory block to the next memory block of said data-protected object that is unaffected by the atomic write operation;
• setting the read-direction status bit and the write-in-progress status bit of said data-protected object to one;
• setting the forward pointer of the previous memory block to point to the first allocated memory block;
• clearing the read-direction status bit of said data-protected object;
• setting the backward pointer of the next memory block to the last allocated memory block;
• and
• clearing the write-in-progress status bit of said data-protected object.

The method of step 33 wherein said step of preparing the allocated memory blocks further comprises the steps of:

• forward linking said allocated memory blocks as required;
• backward linking said allocated memory blocks as required;
• inputting any new data into said allocated memory blocks;
• and
• copying any data from said identified memory blocks of said data-protected object into said allocated memory blocks.

A method for verifying the consistency of each data-protected object of a hierarchical file system during initialization of a limited-resource computer system by detecting whether any data-protected object was subjected to a write-operation interruption and for recovering any data-protected object subject to a write-operation interruption to the state it was in before the write operation was interrupted or to the state it would be in after the write operation was fully executed, comprising the steps of:

• sequentially checking the read-direction and write-in-progress status bits of each data-protected object in the hierarchical file system during initialization of the limited-resource computer system;
• determining whether the read-direction status bit of the checked data-protected object is set;
• if the read-direction status bit of the checked data-protected object is set, using the correct backward pointers of the data-protected object to fix the forward pointers of the data-protected object as required so that the data-protected object is recovered to its state prior to the atomic write operation;
• if the read-direction status bit of the checked data-protected object is not set, determining whether the write-in-progress status bit of the checked data-protected object is set;
• if the write-in-progress status bit of the checked data-protected object is set, using the correct forward pointers of the data-protected object to fix the backward pointers of the data-protected object as required so that the data-protected object is recovered to its state after full execution of the atomic write operation;
• if the write-in-progress status bit of the checked data-protected object is not set, checking the next data-protected file in the hierarchical file system;
• and
• repeating the foregoing steps with respect to the next data-protected object in the hierarchical file system until all data-protected object in the hierarchical file system have been checked.