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        uint16_t    firstc_lo;  /* FAT32 */
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        uint16_t    firstc_lo;  /* FAT32 */
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    };
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    };
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    uint32_t    size;
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    uint32_t    size;
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} __attribute__ ((packed)) fat_dentry_t;
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} __attribute__ ((packed)) fat_dentry_t;
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typedef uint16_t fat_cluster_t;
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typedef enum {
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typedef enum {
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    FAT_INVALID,
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    FAT_INVALID,
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    FAT_DIRECTORY,
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    FAT_DIRECTORY,
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    FAT_FILE
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    FAT_FILE
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} fat_node_type_t;
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} fat_node_type_t;
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struct fat_node;
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/** FAT in-core node. */
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/** FAT index structure.
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 *
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 * This structure exists to help us to overcome certain limitations of the FAT
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 * file system design.  The problem with FAT is that it is hard to find
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 * an entity which could represent a VFS index.  There are two candidates:
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 *
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 * a) number of the node's first cluster
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 * b) the pair of the parent directory's first cluster and the dentry index
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 *    within the parent directory
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 *
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 * We need VFS indices to be:
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 * A) unique
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 * B) stable in time, at least until the next mount
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 *
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 * Unfortunately a) does not meet the A) criterion because zero-length files
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 * will have the first cluster field cleared.  And b) does not meet the B)
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 * criterion because unlink() and rename() will both free up the original
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 * dentry, which contains all the essential info about the file.
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 *
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 * Therefore, a completely opaque indices are used and the FAT server maintains
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 * a mapping between them and otherwise nice b) variant.  On rename(), the VFS
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 * index stays unaltered, while the internal FAT "physical tree address"
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 * changes.  The unlink case is also handled this way thanks to an in-core node
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 * pointer embedded in the index structure.
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 */
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typedef struct {
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typedef struct {
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    dev_handle_t    dev_handle;
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    fs_index_t  index;
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    /**
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     * Parent first cluster.
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     * Zero is used if this node is not linked, in which case nodep must
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     * contain a pointer to the in-core node structure.
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     * One is used when the parent is the root directory.
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     */
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    fat_cluster_t   pfc;
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    /** Parent directory entry index. */
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    unsigned    pdi;
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    /** Protects an instance of this type. */
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    /** Pointer to in-core node instance. */
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    futex_t         lock;
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    struct fat_node *nodep;
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} fat_idx_t;
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/** FAT in-core node. */
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typedef struct fat_node {
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    fat_node_type_t     type;
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    fat_node_type_t     type;
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    /** VFS index is the node's first allocated cluster. */
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    fs_index_t      index;
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    fat_idx_t       *idx;
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    /**
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     *  Node's first cluster.
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    /** VFS index of the parent node. */
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     *  Zero is used for zero-length nodes.
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    fs_index_t      pindex;
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     *  One is used to mark root directory.
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     */
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    dev_handle_t        dev_handle;
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    fat_cluster_t       firstc;
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    /** FAT in-core node hash table link. */
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    /** FAT in-core node hash table link. */
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    link_t          fin_link;
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    link_t          fin_link;
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    /** FAT in-core node free list link. */
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    /** FAT in-core node free list link. */
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    link_t          ffn_link;
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    link_t          ffn_link;
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    size_t          size;
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    size_t          size;