minix/servers/vfs/read.c
Thomas Veerman 13ef7f1f38 Prepare VFS to support back calls from PFS. For security reasons and to support
file descriptor passing, PFS does some back calls to VFS. For example, to
verify the validity of a path provided by a process and to tell VFS it must
copy file descriptors from one process to another.
2010-08-30 13:44:07 +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, 0);
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);
}