minix/servers/vfs/read.c
Ben Gras cef94e096e vfs: make m_out non-global
m_out is shared between threads as the reply message, and it can happen
results get overwritten by another thread before the reply is sent. This
change

	. makes m_out local to the message handling function,
	  declared on the stack of the caller
	. forces callers of reply() to give it a message, or
	  declare the reply message has no significant fields except
	  for the return code by calling replycode()

Change-Id: Id06300083a63c72c00f34f86a5c7d96e4bbdf9f6
2013-04-12 23:40:38 +00:00

347 lines
8.9 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 "scratchpad.h"
#include "param.h"
#include <dirent.h>
#include <assert.h>
#include <minix/vfsif.h>
#include "vnode.h"
#include "vmnt.h"
/*===========================================================================*
* do_read *
*===========================================================================*/
int do_read(message *UNUSED(m_out))
{
return(do_read_write_peek(READING, job_m_in.fd,
job_m_in.buffer, (size_t) job_m_in.nbytes));
}
/*===========================================================================*
* lock_bsf *
*===========================================================================*/
void lock_bsf(void)
{
struct fproc *org_fp;
struct worker_thread *org_self;
if (mutex_trylock(&bsf_lock) == 0)
return;
org_fp = fp;
org_self = self;
if (mutex_lock(&bsf_lock) != 0)
panic("unable to lock block special file lock");
fp = org_fp;
self = 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();
}
/*===========================================================================*
* do_read_write_peek *
*===========================================================================*/
int do_read_write_peek(int rw_flag, int io_fd, char *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(fp).file.fd_nr = io_fd;
scratch(fp).io.io_buffer = io_buf;
scratch(fp).io.io_nbytes = io_nbytes;
locktype = ro ? VNODE_READ : VNODE_WRITE;
if ((f = get_filp(scratch(fp).file.fd_nr, locktype)) == NULL)
return(err_code);
if (((f->filp_mode) & (ro ? R_BIT : W_BIT)) == 0) {
unlock_filp(f);
return(f->filp_mode == FILP_CLOSED ? EIO : EBADF);
}
if (scratch(fp).io.io_nbytes == 0) {
unlock_filp(f);
return(0); /* so char special files need not check for 0*/
}
r = read_write(rw_flag, f, scratch(fp).io.io_buffer, scratch(fp).io.io_nbytes,
who_e);
unlock_filp(f);
return(r);
}
/*===========================================================================*
* read_write *
*===========================================================================*/
int read_write(int rw_flag, struct filp *f, char *buf, size_t size,
endpoint_t for_e)
{
register struct vnode *vp;
u64_t position, res_pos, new_pos;
unsigned int cum_io, cum_io_incr, res_cum_io;
int op, r;
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 ? VFS_DEV_READ : VFS_DEV_WRITE);
if (S_ISFIFO(vp->v_mode)) { /* Pipes */
if (fp->fp_cum_io_partial != 0) {
panic("VFS: read_write: fp_cum_io_partial not clear");
}
if(rw_flag == PEEKING) return EINVAL;
r = rw_pipe(rw_flag, for_e, f, buf, size);
} else if (S_ISCHR(vp->v_mode)) { /* Character special files. */
dev_t dev;
int suspend_reopen;
int op = (rw_flag == READING ? VFS_DEV_READ : VFS_DEV_WRITE);
if(rw_flag == PEEKING) return EINVAL;
if (vp->v_sdev == NO_DEV)
panic("VFS: read_write tries to access char dev NO_DEV");
suspend_reopen = (f->filp_state & FS_NEEDS_REOPEN);
dev = (dev_t) vp->v_sdev;
r = dev_io(op, dev, for_e, buf, position, size, f->filp_flags,
suspend_reopen);
if (r >= 0) {
cum_io = r;
position = add64ul(position, r);
r = OK;
}
} 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");
if(rw_flag == PEEKING) return EINVAL;
lock_bsf();
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 = cvul64(vp->v_size);
}
/* Issue request */
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) {
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 (S_ISREG(vp->v_mode) || S_ISDIR(vp->v_mode)) {
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 == 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(fp->fp_endpoint, SIGPIPE);
}
}
if (r == OK) {
return(cum_io);
}
return(r);
}
/*===========================================================================*
* do_getdents *
*===========================================================================*/
int do_getdents(message *UNUSED(m_out))
{
/* Perform the getdents(fd, buf, size) system call. */
int r = OK;
u64_t new_pos;
register struct filp *rfilp;
scratch(fp).file.fd_nr = job_m_in.fd;
scratch(fp).io.io_buffer = job_m_in.buffer;
scratch(fp).io.io_nbytes = (size_t) job_m_in.nbytes;
/* 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) {
if (ex64hi(rfilp->filp_pos) != 0)
panic("do_getdents: can't handle large offsets");
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;
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;
/* 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 = cvu64(0); /* Not actually used */
/* 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);
}
if (ex64hi(new_pos))
panic("rw_pipe: bad new pos");
cum_io += cum_io_incr;
buf += cum_io_incr;
req_size -= cum_io_incr;
vp->v_size = ex64lo(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);
}