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NAME
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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
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SYNOPSIS
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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);
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DESCRIPTION
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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.
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SOURCE
SEE ALSO
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