minix/servers/vfs/read.c

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/* 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"
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#include "scratchpad.h"
#include "param.h"
#include <dirent.h>
Mostly bugfixes of bugs triggered by the test set. bugfixes: SYSTEM: . removed rc->p_priv->s_flags = 0; for the priv struct shared by all user processes in get_priv(). this should only be done once. doing a SYS_PRIV_USER in sys_privctl() caused the flags of all user processes to be reset, so they were no longer PREEMPTIBLE. this happened when RS executed a policy script. (this broke test1 in the test set) VFS/MFS: . chown can change the mode of a file, and chmod arguments are only part of the full file mode so the full filemode is slightly magic. changed these calls so that the final modes are returned to VFS, so that the vnode can be kept up-to-date. (this broke test11 in the test set) MFS: . lookup() checked for sizeof(string) instead of sizeof(user_path), truncating long path names (caught by test 23) . truncate functions neglected to update ctime (this broke test16) VFS: . corner case of an empty filename lookup caused fields of a request not to be filled in in the lookup functions, not making it clear that the lookup had failed, causing messages to garbage processes, causing strange failures. (caught by test 30) . trust v_size in vnode when doing reads or writes on non-special files, truncating i/o where necessary; this is necessary for pipes, as MFS can't tell when a pipe has been truncated without it being told explicitly each time. when the last reader/writer on a pipe closes, tell FS about the new size using truncate_vn(). (this broke test 25, among others) . permission check for chdir() had disappeared; added a forbidden() call (caught by test 23) new code, shouldn't change anything: . introduced RTS_SET, RTS_UNSET, and RTS_ISSET macro's, and their LOCK variants. These macros set and clear the p_rts_flags field, causing a lot of duplicated logic like old_flags = rp->p_rts_flags; /* save value of the flags */ rp->p_rts_flags &= ~NO_PRIV; if (old_flags != 0 && rp->p_rts_flags == 0) lock_enqueue(rp); to change into the simpler RTS_LOCK_UNSET(rp, NO_PRIV); so the macros take care of calling dequeue() and enqueue() (or lock_*()), as the case may be). This makes the code a bit more readable and a bit less fragile. . removed return code from do_clocktick in CLOCK as it currently never replies . removed some debug code from VFS . fixed grant debug message in device.c preemptive checks, tests, changes: . added return code checks of receive() to SYSTEM and CLOCK . O_TRUNC should never arrive at MFS (added sanity check and removed O_TRUNC code) . user_path declared with PATH_MAX+1 to let it be null-terminated . checks in MFS to see if strings passed by VFS are null-terminated IS: . static irq name table thrown out
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#include <assert.h>
#include <minix/vfsif.h>
#include "vnode.h"
#include "vmnt.h"
/*===========================================================================*
* do_read *
*===========================================================================*/
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int do_read()
{
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return(do_read_write(READING));
}
/*===========================================================================*
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* lock_bsf *
*===========================================================================*/
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void lock_bsf(void)
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{
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 *
*===========================================================================*/
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void unlock_bsf(void)
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{
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();
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}
/*===========================================================================*
* do_read_write *
*===========================================================================*/
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int do_read_write(rw_flag)
int rw_flag; /* READING or WRITING */
{
/* Perform read(fd, buffer, nbytes) or write(fd, buffer, nbytes) call. */
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struct filp *f;
tll_access_t locktype;
int r;
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;
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locktype = (rw_flag == READING) ? VNODE_READ : VNODE_WRITE;
if ((f = get_filp(scratch(fp).file.fd_nr, locktype)) == NULL)
return(err_code);
if (((f->filp_mode) & (rw_flag == READING ? R_BIT : W_BIT)) == 0) {
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unlock_filp(f);
return(f->filp_mode == FILP_CLOSED ? EIO : EBADF);
}
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if (scratch(fp).io.io_nbytes == 0) {
unlock_filp(f);
return(0); /* so char special files need not check for 0*/
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}
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 *
*===========================================================================*/
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int read_write(int rw_flag, struct filp *f, char *buf, size_t size,
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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;
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int op, oflags, r;
position = f->filp_pos;
oflags = f->filp_flags;
vp = f->filp_vno;
r = OK;
cum_io = 0;
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if (size > SSIZE_MAX) return(EINVAL);
if (S_ISFIFO(vp->v_mode)) {
if (fp->fp_cum_io_partial != 0) {
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panic("VFS: read_write: fp_cum_io_partial not clear");
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}
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r = rw_pipe(rw_flag, for_e, f, buf, size);
return(r);
}
op = (rw_flag == READING ? VFS_DEV_READ : VFS_DEV_WRITE);
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if (S_ISCHR(vp->v_mode)) { /* Character special files. */
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dev_t dev;
int suspend_reopen;
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if (vp->v_sdev == NO_DEV)
panic("VFS: read_write tries to access char dev NO_DEV");
VFS: make all IPC asynchronous By decoupling synchronous drivers from VFS, we are a big step closer to supporting driver crashes under all circumstances. That is, VFS can't become stuck on IPC with a synchronous driver (e.g., INET) and can recover from crashing block drivers during open/close/ioctl or during communication with an FS. In order to maintain serialized communication with a synchronous driver, the communication is wrapped by a mutex on a per driver basis (not major numbers as there can be multiple majors with identical endpoints). Majors that share a driver endpoint point to a single mutex object. In order to support crashes from block drivers, the file reopen tactic had to be changed; first reopen files associated with the crashed driver, then send the new driver endpoint to FSes. This solves a deadlock between the FS and the block driver; - VFS would send REQ_NEW_DRIVER to an FS, but he FS only receives it after retrying the current request to the newly started driver. - The block driver would refuse the retried request until all files had been reopened. - VFS would reopen files only after getting a reply from the initial REQ_NEW_DRIVER. When a character special driver crashes, all associated files have to be marked invalid and closed (or reopened if flagged as such). However, they can only be closed if a thread holds exclusive access to it. To obtain exclusive access, the worker thread (which handles the new driver endpoint event from DS) schedules a new job to garbage collect invalid files. This way, we can signal the worker thread that was talking to the crashed driver and will release exclusive access to a file associated with the crashed driver and prevent the garbage collecting worker thread from dead locking on that file. Also, when a character special driver crashes, RS will unmap the driver and remap it upon restart. During unmapping, associated files are marked invalid instead of waiting for an endpoint up event from DS, as that event might come later than new read/write/select requests and thus cause confusion in the freshly started driver. When locking a filp, the usage counters are no longer checked. The usage counter can legally go down to zero during filp invalidation while there are locks pending. DS events are handled by a separate worker thread instead of the main thread as reopening files could lead to another crash and a stuck thread. An additional worker thread is then necessary to unlock it. Finally, with everything asynchronous a race condition in do_select surfaced. A select entry was only marked in use after succesfully sending initial select requests to drivers and having to wait. When multiple select() calls were handled there was opportunity that these entries were overwritten. This had as effect that some select results were ignored (and select() remained blocking instead if returning) or do_select tried to access filps that were not present (because thrown away by secondary select()). This bug manifested itself with sendrecs, but was very hard to reproduce. However, it became awfully easy to trigger with asynsends only.
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suspend_reopen = (f->filp_state & FS_NEEDS_REOPEN);
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dev = (dev_t) vp->v_sdev;
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r = dev_io(op, dev, for_e, buf, position, size, oflags,
suspend_reopen);
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if (r >= 0) {
cum_io = r;
position = add64ul(position, r);
r = OK;
}
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} 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");
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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;
}
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unlock_bsf();
} else { /* Regular files */
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if (rw_flag == WRITING) {
/* Check for O_APPEND flag. */
if (oflags & O_APPEND) position = cvul64(vp->v_size);
}
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/* Issue request */
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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) {
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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;
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if (r == OK) return(cum_io);
return(r);
}
/*===========================================================================*
* do_getdents *
*===========================================================================*/
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int do_getdents()
{
/* Perform the getdents(fd, buf, size) system call. */
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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);
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if (!(rfilp->filp_mode & R_BIT))
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r = EBADF;
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else if (!S_ISDIR(rfilp->filp_vno->v_mode))
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r = EBADF;
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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);
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if (r > 0) rfilp->filp_pos = new_pos;
}
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unlock_filp(rfilp);
return(r);
}
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/*===========================================================================*
* rw_pipe *
*===========================================================================*/
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int rw_pipe(rw_flag, usr_e, f, buf, req_size)
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int rw_flag; /* READING or WRITING */
endpoint_t usr_e;
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struct filp *f;
char *buf;
size_t req_size;
{
int r, oflags, partial_pipe = 0;
size_t size, cum_io, cum_io_incr;
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struct vnode *vp;
u64_t position, new_pos;
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/* Must make sure we're operating on locked filp and vnode */
VFS: fix locking bugs .sync and fsync used unnecessarily restrictive locking type .fsync violated locking order by obtaining a vmnt lock after a filp lock .fsync contained a TOCTOU bug .new_node violated locking rules (didn't upgrade lock upon file creation) .do_pipe used unnecessarily restrictive locking type .always lock pipes exclusively; even a read operation might require to do a write on a vnode object (update pipe size) .when opening a file with O_TRUNC, upgrade vnode lock when truncating .utime used unnecessarily restrictive locking type .path parsing: .always acquire VMNT_WRITE or VMNT_EXCL on vmnt and downgrade to VMNT_READ if that was what was actually requested. This prevents the following deadlock scenario: thread A: lock_vmnt(vmp, TLL_READSER); lock_vnode(vp, TLL_READSER); upgrade_vmnt_lock(vmp, TLL_WRITE); thread B: lock_vmnt(vmp, TLL_READ); lock_vnode(vp, TLL_READSER); thread A will be stuck in upgrade_vmnt_lock and thread B is stuck in lock_vnode. This happens when, for example, thread A tries create a new node (open.c:new_node) and thread B tries to do eat_path to change dir (stadir.c:do_chdir). When the path is being resolved, a vnode is always locked with VNODE_OPCL (TLL_READSER) and then downgraded to VNODE_READ if read-only is actually requested. Thread A locks the vmnt with VMNT_WRITE (TLL_READSER) which still allows VMNT_READ locks. Thread B can't acquire a lock on the vnode because thread A has it; Thread A can't upgrade its vmnt lock to VMNT_WRITE (TLL_WRITE) because thread B has a VMNT_READ lock on it. By serializing vmnt locks during path parsing, thread B can only acquire a lock on vmp when thread A has completely finished its operation.
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assert(tll_locked_by_me(&f->filp_vno->v_lock));
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assert(mutex_trylock(&f->filp_lock) == -EDEADLK);
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oflags = f->filp_flags;
vp = f->filp_vno;
position = cvu64(0); /* Not actually used */
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/* fp->fp_cum_io_partial is only nonzero when doing partial writes */
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cum_io = fp->fp_cum_io_partial;
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r = pipe_check(vp, rw_flag, oflags, req_size, 0);
if (r <= 0) {
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if (r == SUSPEND) pipe_suspend(f, buf, req_size);
return(r);
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}
size = r;
if (size < req_size) partial_pipe = 1;
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/* Truncate read request at size. */
if (rw_flag == READING && size > vp->v_size) {
size = vp->v_size;
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}
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if (vp->v_mapfs_e == 0)
panic("unmapped pipe");
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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);
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}
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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);
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}
}
fp->fp_cum_io_partial = 0;
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return(cum_io);
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}