minix/servers/vfs/read.c
2010-05-10 13:26:00 +00:00

282 lines
7.3 KiB
C

/* This file contains the heart of the mechanism used to read (and write)
* files. Read and write requests are split up into chunks that do not cross
* block boundaries. Each chunk is then processed in turn. Reads on special
* files are also detected and handled.
*
* The entry points into this file are
* do_read: perform the READ system call by calling read_write
* do_getdents: read entries from a directory (GETDENTS)
* read_write: actually do the work of READ and WRITE
*
*/
#include "fs.h"
#include <fcntl.h>
#include <unistd.h>
#include <minix/com.h>
#include <minix/u64.h>
#include "file.h"
#include "fproc.h"
#include "param.h"
#include <dirent.h>
#include <assert.h>
#include <minix/vfsif.h>
#include "vnode.h"
#include "vmnt.h"
/*===========================================================================*
* do_read *
*===========================================================================*/
PUBLIC int do_read()
{
return(read_write(READING));
}
/*===========================================================================*
* read_write *
*===========================================================================*/
PUBLIC int read_write(rw_flag)
int rw_flag; /* READING or WRITING */
{
/* Perform read(fd, buffer, nbytes) or write(fd, buffer, nbytes) call. */
register struct filp *f;
register struct vnode *vp;
u64_t position, res_pos, new_pos;
unsigned int cum_io, cum_io_incr, res_cum_io;
int op, oflags, r, block_spec, char_spec;
int regular;
mode_t mode_word;
/* If the file descriptor is valid, get the vnode, size and mode. */
if (m_in.nbytes < 0) return(EINVAL);
if ((f = get_filp(m_in.fd)) == NULL) return(err_code);
if (((f->filp_mode) & (rw_flag == READING ? R_BIT : W_BIT)) == 0) {
return(f->filp_mode == FILP_CLOSED ? EIO : EBADF);
}
if (m_in.nbytes == 0)
return(0); /* so char special files need not check for 0*/
position = f->filp_pos;
oflags = f->filp_flags;
vp = f->filp_vno;
r = OK;
cum_io = 0;
if (vp->v_pipe == I_PIPE) {
if (fp->fp_cum_io_partial != 0) {
panic("read_write: fp_cum_io_partial not clear");
}
return rw_pipe(rw_flag, who_e, m_in.fd, f, m_in.buffer, m_in.nbytes);
}
op = (rw_flag == READING ? VFS_DEV_READ : VFS_DEV_WRITE);
mode_word = vp->v_mode & I_TYPE;
regular = mode_word == I_REGULAR;
if ((char_spec = (mode_word == I_CHAR_SPECIAL ? 1 : 0))) {
if (vp->v_sdev == NO_DEV)
panic("read_write tries to read from character device NO_DEV");
}
if ((block_spec = (mode_word == I_BLOCK_SPECIAL ? 1 : 0))) {
if (vp->v_sdev == NO_DEV)
panic("read_write tries to read from block device NO_DEV");
}
if (char_spec) { /* Character special files. */
dev_t dev;
int suspend_reopen;
suspend_reopen = (f->filp_state != FS_NORMAL);
dev = (dev_t) vp->v_sdev;
r = dev_io(op, dev, who_e, m_in.buffer, position, m_in.nbytes, oflags,
suspend_reopen);
if (r >= 0) {
cum_io = r;
position = add64ul(position, r);
r = OK;
}
} else if (block_spec) { /* Block special files. */
r = req_breadwrite(vp->v_bfs_e, who_e, vp->v_sdev, position,
m_in.nbytes, m_in.buffer, rw_flag, &res_pos, &res_cum_io);
if (r == OK) {
position = res_pos;
cum_io += res_cum_io;
}
} else { /* Regular files */
if (rw_flag == WRITING && block_spec == 0) {
/* Check for O_APPEND flag. */
if (oflags & O_APPEND) position = cvul64(vp->v_size);
}
/* Issue request */
r = req_readwrite(vp->v_fs_e, vp->v_inode_nr, position, rw_flag, who_e,
m_in.buffer, m_in.nbytes, &new_pos, &cum_io_incr);
if (r >= 0) {
if (ex64hi(new_pos))
panic("read_write: bad new pos");
position = new_pos;
cum_io += cum_io_incr;
}
}
/* On write, update file size and access time. */
if (rw_flag == WRITING) {
if (regular || mode_word == I_DIRECTORY) {
if (cmp64ul(position, vp->v_size) > 0) {
if (ex64hi(position) != 0) {
panic("read_write: file size too big ");
}
vp->v_size = ex64lo(position);
}
}
}
f->filp_pos = position;
if (r == OK) return(cum_io);
return(r);
}
/*===========================================================================*
* do_getdents *
*===========================================================================*/
PUBLIC int do_getdents()
{
/* Perform the getdents(fd, buf, size) system call. */
int r;
u64_t new_pos;
register struct filp *rfilp;
/* Is the file descriptor valid? */
if ( (rfilp = get_filp(m_in.fd)) == NULL) {
return(err_code);
}
if (!(rfilp->filp_mode & R_BIT))
return(EBADF);
if ((rfilp->filp_vno->v_mode & I_TYPE) != I_DIRECTORY)
return(EBADF);
if (ex64hi(rfilp->filp_pos) != 0)
panic("do_getdents: should handle large offsets");
r = req_getdents(rfilp->filp_vno->v_fs_e, rfilp->filp_vno->v_inode_nr,
rfilp->filp_pos, m_in.buffer, m_in.nbytes, &new_pos);
if (r > 0)
rfilp->filp_pos = new_pos;
return(r);
}
/*===========================================================================*
* rw_pipe *
*===========================================================================*/
PUBLIC int rw_pipe(rw_flag, usr_e, fd_nr, f, buf, req_size)
int rw_flag; /* READING or WRITING */
endpoint_t usr_e;
int fd_nr;
struct filp *f;
char *buf;
size_t req_size;
{
int r, oflags, partial_pipe = 0;
size_t size, cum_io, cum_io_incr;
struct vnode *vp;
u64_t position, new_pos;
oflags = f->filp_flags;
vp = f->filp_vno;
position = cvu64((rw_flag == READING) ? vp->v_pipe_rd_pos :
vp->v_pipe_wr_pos);
/* fp->fp_cum_io_partial is only nonzero when doing partial writes */
cum_io = fp->fp_cum_io_partial;
r = pipe_check(vp, rw_flag, oflags, req_size, position, 0);
if (r <= 0) {
if (r == SUSPEND) pipe_suspend(rw_flag, fd_nr, buf, req_size);
return(r);
}
size = r;
if (size < req_size) partial_pipe = 1;
/* Truncate read request at size. */
if((rw_flag == READING) &&
cmp64ul(add64ul(position, size), vp->v_size) > 0) {
/* Position always should fit in an off_t (LONG_MAX). */
off_t pos32;
assert(cmp64ul(position, LONG_MAX) <= 0);
pos32 = cv64ul(position);
assert(pos32 >= 0);
assert(pos32 <= LONG_MAX);
size = vp->v_size - pos32;
}
if (vp->v_mapfs_e == 0)
panic("unmapped pipe");
r = req_readwrite(vp->v_mapfs_e, vp->v_mapinode_nr, position, rw_flag, usr_e,
buf, size, &new_pos, &cum_io_incr);
if (r >= 0) {
if (ex64hi(new_pos))
panic("rw_pipe: bad new pos");
position = new_pos;
cum_io += cum_io_incr;
buf += cum_io_incr;
req_size -= cum_io_incr;
}
/* On write, update file size and access time. */
if (rw_flag == WRITING) {
if (cmp64ul(position, vp->v_size) > 0) {
if (ex64hi(position) != 0) {
panic("read_write: file size too big for v_size");
}
vp->v_size = ex64lo(position);
}
} else {
if (cmp64ul(position, vp->v_size) >= 0) {
/* Reset pipe pointers */
vp->v_size = 0;
vp->v_pipe_rd_pos= 0;
vp->v_pipe_wr_pos= 0;
position = cvu64(0);
}
}
if (rw_flag == READING)
vp->v_pipe_rd_pos= cv64ul(position);
else
vp->v_pipe_wr_pos= cv64ul(position);
if (r == OK) {
if (partial_pipe) {
/* partial write on pipe with */
/* O_NONBLOCK, return write count */
if (!(oflags & O_NONBLOCK)) {
/* partial write on pipe with req_size > PIPE_SIZE,
* non-atomic
*/
fp->fp_cum_io_partial = cum_io;
pipe_suspend(rw_flag, fd_nr, buf, req_size);
return(SUSPEND);
}
}
fp->fp_cum_io_partial = 0;
return(cum_io);
}
return(r);
}