VENTI-FILE(3)

NAME
VtFile, vtfileblock, vtfileblockscore, vtfileclose, vtfilecreate, vtfilecreateroot, vtfileflush, vtfileflushbefore, vtfilegetdirsize, vtfilegetentry, vtfilegetsize, vtfileincref, vtfilelock, vtfilelock2, vtfileopen, vtfileopenroot, vtfileread, vtfileremove, vtfilesetdirsize, vtfilesetentry, vtfilesetsize, vtfiletruncate, vtfileunlock, vtfilewrite - Venti files

SYNOPSIS

VtFile*    vtfilecreateroot(VtCache *c, int psize, int dsize, int type);

VtFile*    vtfileopenroot(VtCache *c, VtEntry *e);

VtFile*    vtfileopen(VtFile *f, u32int n, int mode);

VtFile*    vtfilecreate(VtFile *f, int psize, int dsize, int type);

void    vtfileincref(VtFile *f);

void    vtfileclose(VtFile *f);

int    vtfileremove(VtFile *f);

VtBlock*    vtfileblock(VtFile *f, u32int n, int mode);

long    vtfileread(VtFile *f, void *buf, long n, vlong offset);

long    vtfilewrite(VtFile *f, void *buf, long n, vlong offset);

int    vtfileflush(VtFile *f);

int    vtfileflushbefore(VtFile *f, vlong offset);

int    vtfiletruncate(VtFile *f);

uvlong    vtfilegetsize(VtFile *f);

int    vtfilesetsize(VtFile *f, vlong size);

u32int    vtfilegetdirsize(VtFile *f);

int    vtfilesetdirsize(VtFile *f, u32int size);

int    vtfilegetentry(VtFile *f, VtEntry *e);

int    vtfilesetentry(VtFile *f, VtEntry *e);

int    vtfileblockscore(VtFile *f, u32int n,
        uchar score[VtScoreSize]);

int    vtfilelock(VtFile *f, int mode);

int    vtfilelock2(VtFile *f, VtFile *f, int mode);

void    vtfileunlock(VtFile *f);

DESCRIPTION
These routines provide a simple interface to create and manipulate Venti file trees (see venti(7)).

Vtfilecreateroot creates a new Venti file. Type must be either VtDataType or VtDirType, specifying a data or directory file. Dsize is the block size to use for leaf (data or directory) blocks in the hash tree; psize is the block size to use for internal (pointer) blocks.

Vtfileopenroot opens an existing Venti file described by e.

Vtfileopen opens the Venti file described by the nth entry in the directory f. Mode should be one of VtOREAD, VtOWRITE, or VtORDWR, indicating how the returned file is to be used. The VtOWRITE and VtORDWR modes can only be used if f is open with mode VtORDWR.

Vtfilecreate creates a new file in the directory f with block type type and block sizes dsize and psize (see vtfilecreateroot above).

Each file has an associated reference count and holds a reference to its parent in the file tree. Vtfileincref increments this reference count. Vtfileclose decrements the reference count. If there are no other references, vtfileclose releases the reference to f's parent and then frees the in-memory structure f. The data stored in f is still accessible by reopening it.

Vtfileremove removes the file f from its parent directory. It also acts as vtfileclose, releasing the reference to f and potentially freeing the structure.

Vtfileblock returns the nth block in the file f. If there are not n blocks in the file and mode is VtOREAD, vtfileblock returns nil. If the mode is VtOWRITE or VtORDWR, vtfileblock grows the file as needed and then returns the block.

Vtfileread reads at most n bytes at offset offset from f into memory at buf. It returns the number of bytes read.

Vtfilewrite writes the n bytes in memory at buf into the file f at offset n. It returns the number of bytes written, or -1 on error. Writing fewer bytes than requested will only happen if an error is encountered.

Vtfilewrite writes to an in-memory copy of the data blocks (see venti-cache(3)) instead of writing directly to Venti. Vtfileflush writes all copied blocks associated with f to the Venti server. Vtfileflushbefore flushes only those blocks corresponding to data in the file before byte offset. Loops that vtfilewrite should call vtfileflushbefore regularly to avoid filling the block cache with unwritten blocks.

Vtfiletruncate changes the file f to have zero length.

Vtfilegetsize returns the length (in bytes) of file f.

Vtfilesetsize sets the length (in bytes) of file f.

Vtfilegetdirsize returns the length (in directory entries) of the directory f.

Vtfilesetdirsize sets the length (in directory entries) of the directory f.

Vtfilegetentry fills e with an entry that can be passed to vtfileopenroot to reopen f at a later time.

Vtfilesetentry sets the entry associated with f to be e.

Vtfileblockscore returns in score the score of the nth block in the file f.

Venti files are locked and unlocked via vtfilelock and vtfileunlock to moderate concurrent access. Only one thread at a time—the one that has the file locked—can read or modify the file. The functions that return files (vtfilecreateroot, vtfileopenroot, vtfilecreate, and vtfileopen) return them unlocked. When files are passed to any of the functions documented in this manual page, it is the caller's responsibility to ensure that they are already locked.

Internally, a file is locked by locking the block that contains its directory entry. When two files in the same directory both need to be locked, vtfilelock2 must be used. It locks both its arguments, taking special care not to deadlock if their entries are stored in the same directory block.

SOURCE
/usr/local/plan9/src/libventi/file.c

SEE ALSO
venti-cache(3), venti-conn(3), venti-client(3), venti(7)