term% cat index.txt VENTI-FILE(2) System Calls Manual VENTI-FILE(2)
NAME
VtFile, vtfileblock, vtfileblockscore, vtfileclose, vtfilecreate, vt‐
filecreateroot, vtfileflush, vtfileflushbefore, vtfilegetdirsize, vtfi‐
legetentry, vtfilegetsize, vtfileincref, vtfilelock, vtfilelock2, vt‐
fileopen, vtfileopenroot, vtfileread, vtfileremove, vtfilesetdirsize,
vtfilesetentry, vtfilesetsize, vtfiletruncate, vtfileunlock, vt‐
filewrite - 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(6)).
Vtfilecreateroot creates a new Venti file. Type must be either Vt‐
DataType 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 di‐
rectory f. Mode should be one of VtOREAD, VtOWRITE, or VtORDWR, indi‐
cating 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 free‐
ing 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 off‐
set n. It returns the number of bytes written, or -1 on error. Writ‐
ing fewer bytes than requested will only happen if an error is encoun‐
tered.
Vtfilewrite writes to an in-memory copy of the data blocks (see venti-
cache(2)) 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 di‐
rectory f.
Vtfilesetdirsize sets the length (in directory entries) of the direc‐
tory f.
Vtfilegetentry fills e with an entry that can be passed to vtfileopen‐
root 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 di‐
rectory 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
/sys/src/libventi/file.c
SEE ALSO
venti-cache(2), venti-conn(2), venti-client(2), venti(6)
VENTI-FILE(2)