minix/servers/vfs/read.c
Lionel Sambuc 7031438f58 Message type and related cleanup
- Intorduce and use a message type for VFS_GETDENTS, VFS_READ,
   VFS_WRITE.

 - Some cleanup to related functions where vir_bytes are replaced (and
   casted to/from, in parameter definition and local variables as well.

   This allow to see more clearly which function receives unsafe
   (pointer) values, or at least values which are not supposed to be
   valid in the address space of VFS. The current patch does so only
   for the minimal amount of functions which are concerned with the
   introduction of the new message type.

Change-Id: I0cdca97409c4016d02fae067b48bf55d37572c5c
2014-07-28 17:05:34 +02:00

376 lines
10 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 <minix/callnr.h>
#include <minix/com.h>
#include <minix/u64.h>
#include <minix/vfsif.h>
#include <assert.h>
#include <sys/dirent.h>
#include <fcntl.h>
#include <unistd.h>
#include "file.h"
#include "scratchpad.h"
#include "vnode.h"
#include "vmnt.h"
/*===========================================================================*
* do_read *
*===========================================================================*/
int do_read(void)
{
return(do_read_write_peek(READING, job_m_in.m_lc_vfs_readwrite.fd,
job_m_in.m_lc_vfs_readwrite.buf, job_m_in.m_lc_vfs_readwrite.len));
}
/*===========================================================================*
* lock_bsf *
*===========================================================================*/
void lock_bsf(void)
{
struct worker_thread *org_self;
if (mutex_trylock(&bsf_lock) == 0)
return;
org_self = worker_suspend();
if (mutex_lock(&bsf_lock) != 0)
panic("unable to lock block special file lock");
worker_resume(org_self);
}
/*===========================================================================*
* unlock_bsf *
*===========================================================================*/
void unlock_bsf(void)
{
if (mutex_unlock(&bsf_lock) != 0)
panic("failed to unlock block special file lock");
}
/*===========================================================================*
* check_bsf *
*===========================================================================*/
void check_bsf_lock(void)
{
int r = mutex_trylock(&bsf_lock);
if (r == -EBUSY)
panic("bsf_lock locked");
else if (r != 0)
panic("bsf_lock weird state");
/* r == 0 */
unlock_bsf();
}
/*===========================================================================*
* actual_read_write_peek *
*===========================================================================*/
int actual_read_write_peek(struct fproc *rfp, int rw_flag, int io_fd,
vir_bytes io_buf, size_t io_nbytes)
{
/* Perform read(fd, buffer, nbytes) or write(fd, buffer, nbytes) call. */
struct filp *f;
tll_access_t locktype;
int r;
int ro = 1;
if(rw_flag == WRITING) ro = 0;
scratch(rfp).file.fd_nr = io_fd;
scratch(rfp).io.io_buffer = io_buf;
scratch(rfp).io.io_nbytes = io_nbytes;
locktype = rw_flag == WRITING ? VNODE_WRITE : VNODE_READ;
if ((f = get_filp2(rfp, scratch(rfp).file.fd_nr, locktype)) == NULL)
return(err_code);
assert(f->filp_count > 0);
if (((f->filp_mode) & (ro ? R_BIT : W_BIT)) == 0) {
unlock_filp(f);
return(EBADF);
}
if (scratch(rfp).io.io_nbytes == 0) {
unlock_filp(f);
return(0); /* so char special files need not check for 0*/
}
r = read_write(rfp, rw_flag, f, scratch(rfp).io.io_buffer,
scratch(rfp).io.io_nbytes, who_e);
unlock_filp(f);
return(r);
}
/*===========================================================================*
* do_read_write_peek *
*===========================================================================*/
int do_read_write_peek(int rw_flag, int io_fd, vir_bytes io_buf, size_t io_nbytes)
{
return actual_read_write_peek(fp, rw_flag, io_fd, io_buf, io_nbytes);
}
/*===========================================================================*
* read_write *
*===========================================================================*/
int read_write(struct fproc *rfp, int rw_flag, struct filp *f,
vir_bytes buf, size_t size, endpoint_t for_e)
{
register struct vnode *vp;
off_t position, res_pos;
unsigned int cum_io, cum_io_incr, res_cum_io;
int op, r;
dev_t dev;
position = f->filp_pos;
vp = f->filp_vno;
r = OK;
cum_io = 0;
assert(rw_flag == READING || rw_flag == WRITING || rw_flag == PEEKING);
if (size > SSIZE_MAX) return(EINVAL);
op = (rw_flag == READING ? CDEV_READ : CDEV_WRITE);
if (S_ISFIFO(vp->v_mode)) { /* Pipes */
if (rfp->fp_cum_io_partial != 0) {
panic("VFS: read_write: fp_cum_io_partial not clear");
}
if(rw_flag == PEEKING) {
printf("read_write: peek on pipe makes no sense\n");
return EINVAL;
}
r = rw_pipe(rw_flag, for_e, f, buf, size);
} else if (S_ISCHR(vp->v_mode)) { /* Character special files. */
if(rw_flag == PEEKING) {
printf("read_write: peek on char device makes no sense\n");
return EINVAL;
}
if (vp->v_sdev == NO_DEV)
panic("VFS: read_write tries to access char dev NO_DEV");
dev = vp->v_sdev;
r = cdev_io(op, dev, for_e, buf, position, size, f->filp_flags);
if (r >= 0) {
/* This should no longer happen: all calls are asynchronous. */
printf("VFS: I/O to device %llx succeeded immediately!?\n", dev);
cum_io = r;
position += r;
r = OK;
} else if (r == SUSPEND) {
/* FIXME: multiple read/write operations on a single filp
* should be serialized. They currently aren't; in order to
* achieve a similar effect, we optimistically advance the file
* position here. This works under the following assumptions:
* - character drivers that use the seek position at all,
* expose a view of a statically-sized range of bytes, i.e.,
* they are basically byte-granular block devices;
* - if short I/O or an error is returned, all subsequent calls
* will return (respectively) EOF and an error;
* - the application never checks its own file seek position,
* or does not care that it may end up having seeked beyond
* the number of bytes it has actually read;
* - communication to the character driver is FIFO (this one
* is actually true! whew).
* Many improvements are possible here, but in the end,
* anything short of queuing concurrent operations will be
* suboptimal - so we settle for this hack for now.
*/
position += size;
}
} else if (S_ISBLK(vp->v_mode)) { /* Block special files. */
if (vp->v_sdev == NO_DEV)
panic("VFS: read_write tries to access block dev NO_DEV");
lock_bsf();
if(rw_flag == PEEKING) {
r = req_bpeek(vp->v_bfs_e, vp->v_sdev, position, size);
} else {
r = req_breadwrite(vp->v_bfs_e, for_e, vp->v_sdev, position,
size, buf, rw_flag, &res_pos, &res_cum_io);
if (r == OK) {
position = res_pos;
cum_io += res_cum_io;
}
}
unlock_bsf();
} else { /* Regular files */
if (rw_flag == WRITING) {
/* Check for O_APPEND flag. */
if (f->filp_flags & O_APPEND) position = vp->v_size;
}
/* Issue request */
if(rw_flag == PEEKING) {
r = req_peek(vp->v_fs_e, vp->v_inode_nr, position, size);
} else {
off_t new_pos;
r = req_readwrite(vp->v_fs_e, vp->v_inode_nr, position,
rw_flag, for_e, buf, size, &new_pos,
&cum_io_incr);
if (r >= 0) {
position = new_pos;
cum_io += cum_io_incr;
}
}
}
/* On write, update file size and access time. */
if (rw_flag == WRITING) {
if (S_ISREG(vp->v_mode) || S_ISDIR(vp->v_mode)) {
if (position > vp->v_size) {
vp->v_size = position;
}
}
}
f->filp_pos = position;
if (r == EPIPE && rw_flag == WRITING) {
/* Process is writing, but there is no reader. Tell the kernel to
* generate s SIGPIPE signal.
*/
if (!(f->filp_flags & O_NOSIGPIPE)) {
sys_kill(rfp->fp_endpoint, SIGPIPE);
}
}
if (r == OK) {
return(cum_io);
}
return(r);
}
/*===========================================================================*
* do_getdents *
*===========================================================================*/
int do_getdents(void)
{
/* Perform the getdents(fd, buf, size) system call. */
int r = OK;
off_t new_pos;
register struct filp *rfilp;
scratch(fp).file.fd_nr = job_m_in.m_lc_vfs_readwrite.fd;
scratch(fp).io.io_buffer = job_m_in.m_lc_vfs_readwrite.buf;
scratch(fp).io.io_nbytes = job_m_in.m_lc_vfs_readwrite.len;
/* Is the file descriptor valid? */
if ( (rfilp = get_filp(scratch(fp).file.fd_nr, VNODE_READ)) == NULL)
return(err_code);
if (!(rfilp->filp_mode & R_BIT))
r = EBADF;
else if (!S_ISDIR(rfilp->filp_vno->v_mode))
r = EBADF;
if (r == OK) {
r = req_getdents(rfilp->filp_vno->v_fs_e, rfilp->filp_vno->v_inode_nr,
rfilp->filp_pos, scratch(fp).io.io_buffer,
scratch(fp).io.io_nbytes, &new_pos, 0);
if (r > 0) rfilp->filp_pos = new_pos;
}
unlock_filp(rfilp);
return(r);
}
/*===========================================================================*
* rw_pipe *
*===========================================================================*/
int rw_pipe(rw_flag, usr_e, f, buf, req_size)
int rw_flag; /* READING or WRITING */
endpoint_t usr_e;
struct filp *f;
vir_bytes buf;
size_t req_size;
{
int r, oflags, partial_pipe = 0;
size_t size, cum_io, cum_io_incr;
struct vnode *vp;
off_t position, new_pos;
/* Must make sure we're operating on locked filp and vnode */
assert(tll_locked_by_me(&f->filp_vno->v_lock));
assert(mutex_trylock(&f->filp_lock) == -EDEADLK);
oflags = f->filp_flags;
vp = f->filp_vno;
position = 0; /* Not actually used */
assert(rw_flag == READING || rw_flag == WRITING);
/* fp->fp_cum_io_partial is only nonzero when doing partial writes */
cum_io = fp->fp_cum_io_partial;
r = pipe_check(f, rw_flag, oflags, req_size, 0);
if (r <= 0) {
if (r == SUSPEND) pipe_suspend(f, buf, req_size);
return(r);
}
size = r;
if (size < req_size) partial_pipe = 1;
/* Truncate read request at size. */
if (rw_flag == READING && size > vp->v_size) {
size = vp->v_size;
}
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 != OK) {
return(r);
}
cum_io += cum_io_incr;
buf += cum_io_incr;
req_size -= cum_io_incr;
vp->v_size = new_pos;
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(f, buf, req_size);
return(SUSPEND);
}
}
fp->fp_cum_io_partial = 0;
return(cum_io);
}