VENTI-FILE(3) 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 off-
set);
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);
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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 direc-
tory 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 ref-
erence to its parent in the file tree. Vtfileincref incre-
ments this reference count. Vtfileclose decrements the ref-
erence 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
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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 regu-
larly 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 mod-
ify 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 con-
tains 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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VENTI-FILE(3) VENTI-FILE(3)
SOURCE
/usr/local/plan9/src/libventi/file.c
SEE ALSO
venti-cache(3), venti-conn(3), venti-client(3), venti(7)
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