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authorRobert Morris <[email protected]>2014-08-27 17:15:30 -0400
committerRobert Morris <[email protected]>2014-08-27 17:15:30 -0400
commit71453f72f285a17ccf0520b9dbdafdc701ff2f4a (patch)
tree978d30844e643e67a807a73db20ccc5d2823f8f2
parent2c56547272e43b483d560a61692f1e24926a82fb (diff)
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a start at concurrent FS system calls
-rw-r--r--defs.h4
-rw-r--r--exec.c8
-rw-r--r--file.c8
-rw-r--r--log.c82
-rw-r--r--proc.c4
-rw-r--r--sysfile.c50
6 files changed, 95 insertions, 61 deletions
diff --git a/defs.h b/defs.h
index 23b1019..560b19a 100644
--- a/defs.h
+++ b/defs.h
@@ -81,8 +81,8 @@ void microdelay(int);
// log.c
void initlog(void);
void log_write(struct buf*);
-void begin_trans();
-void commit_trans();
+void begin_op();
+void end_op();
// mp.c
extern int ismp;
diff --git a/exec.c b/exec.c
index 7eaef5b..8dbbdb6 100644
--- a/exec.c
+++ b/exec.c
@@ -18,9 +18,9 @@ exec(char *path, char **argv)
struct proghdr ph;
pde_t *pgdir, *oldpgdir;
- begin_trans();
+ begin_op();
if((ip = namei(path)) == 0){
- commit_trans();
+ end_op();
return -1;
}
ilock(ip);
@@ -50,7 +50,7 @@ exec(char *path, char **argv)
goto bad;
}
iunlockput(ip);
- commit_trans();
+ end_op();
ip = 0;
// Allocate two pages at the next page boundary.
@@ -101,7 +101,7 @@ exec(char *path, char **argv)
freevm(pgdir);
if(ip){
iunlockput(ip);
- commit_trans();
+ end_op();
}
return -1;
}
diff --git a/file.c b/file.c
index 53c5af2..98cad1e 100644
--- a/file.c
+++ b/file.c
@@ -72,9 +72,9 @@ fileclose(struct file *f)
if(ff.type == FD_PIPE)
pipeclose(ff.pipe, ff.writable);
else if(ff.type == FD_INODE){
- begin_trans();
+ begin_op();
iput(ff.ip);
- commit_trans();
+ end_op();
}
}
@@ -136,12 +136,12 @@ filewrite(struct file *f, char *addr, int n)
if(n1 > max)
n1 = max;
- begin_trans();
+ begin_op();
ilock(f->ip);
if ((r = writei(f->ip, addr + i, f->off, n1)) > 0)
f->off += r;
iunlock(f->ip);
- commit_trans();
+ end_op();
if(r < 0)
break;
diff --git a/log.c b/log.c
index 95cc4d5..159df98 100644
--- a/log.c
+++ b/log.c
@@ -5,18 +5,22 @@
#include "fs.h"
#include "buf.h"
-// Simple logging. Each file system system call
-// should be surrounded with begin_trans() and commit_trans() calls.
+// Simple logging that allows concurrent FS system calls.
//
-// The log holds at most one transaction at a time. Commit forces
-// the log (with commit record) to disk, then installs the affected
-// blocks to disk, then erases the log. begin_trans() ensures that
-// only one system call can be in a transaction; others must wait.
-//
-// Allowing only one transaction at a time means that the file
-// system code doesn't have to worry about the possibility of
-// one transaction reading a block that another one has modified,
-// for example an i-node block.
+// A log transaction contains the updates of *multiple* FS system
+// calls. The logging systems only commits when there are
+// no FS system calls active. Thus there is never
+// any reasoning required about whether a commit might
+// write an uncommitted system call's updates to disk.
+//
+// A system call should call begin_op()/end_op() to mark
+// its start and end. Usually begin_op() just increments
+// the count of in-progress FS system calls and returns.
+// But if it thinks the log is close to running out, it
+// blocks this system call, and causes the system to wait
+// until end_op() indicates there are no executing FS
+// system calls, at which point the last end_op() commits
+// all the system calls' writes.
//
// The log is a physical re-do log containing disk blocks.
// The on-disk log format:
@@ -38,13 +42,15 @@ struct log {
struct spinlock lock;
int start;
int size;
- int busy; // a transaction is active
+ int outstanding; // how many FS sys calls are executing.
+ int committing; // in commit(), please wait.
int dev;
struct logheader lh;
};
struct log log;
static void recover_from_log(void);
+static void commit();
void
initlog(void)
@@ -117,19 +123,52 @@ recover_from_log(void)
write_head(); // clear the log
}
+// an FS system call should call begin_op() when it starts.
void
-begin_trans(void)
+begin_op(void)
{
acquire(&log.lock);
- while (log.busy) {
- sleep(&log, &log.lock);
+ while(1){
+ if(log.committing){
+ sleep(&log, &log.lock);
+ } else {
+ // XXX wait (for a commit) if log is longish.
+ // need to reserve to avoid over-commit of log space.
+ log.outstanding += 1;
+ release(&log.lock);
+ break;
+ }
}
- log.busy = 1;
- release(&log.lock);
}
+// an FS system call should call end_op() after it finishes.
+// can't write the disk &c while holding locks, thus do_commit.
void
-commit_trans(void)
+end_op(void)
+{
+ int do_commit = 0;
+
+ acquire(&log.lock);
+ log.outstanding -= 1;
+ if(log.committing)
+ panic("log.committing");
+ if(log.outstanding == 0){
+ do_commit = 1;
+ log.committing = 1;
+ }
+ release(&log.lock);
+
+ if(do_commit){
+ commit();
+ acquire(&log.lock);
+ log.committing = 0;
+ wakeup(&log);
+ release(&log.lock);
+ }
+}
+
+static void
+commit()
{
if (log.lh.n > 0) {
write_head(); // Write header to disk -- the real commit
@@ -137,11 +176,6 @@ commit_trans(void)
log.lh.n = 0;
write_head(); // Erase the transaction from the log
}
-
- acquire(&log.lock);
- log.busy = 0;
- wakeup(&log);
- release(&log.lock);
}
// Caller has modified b->data and is done with the buffer.
@@ -159,7 +193,7 @@ log_write(struct buf *b)
if (log.lh.n >= LOGSIZE || log.lh.n >= log.size - 1)
panic("too big a transaction");
- if (!log.busy)
+ if (log.outstanding < 1)
panic("write outside of trans");
for (i = 0; i < log.lh.n; i++) {
diff --git a/proc.c b/proc.c
index db0e9c7..a642f5a 100644
--- a/proc.c
+++ b/proc.c
@@ -186,9 +186,9 @@ exit(void)
}
}
- begin_trans();
+ begin_op();
iput(proc->cwd);
- commit_trans();
+ end_op();
proc->cwd = 0;
acquire(&ptable.lock);
diff --git a/sysfile.c b/sysfile.c
index 095fca7..2209f6e 100644
--- a/sysfile.c
+++ b/sysfile.c
@@ -121,16 +121,16 @@ sys_link(void)
if(argstr(0, &old) < 0 || argstr(1, &new) < 0)
return -1;
- begin_trans();
+ begin_op();
if((ip = namei(old)) == 0){
- commit_trans();
+ end_op();
return -1;
}
ilock(ip);
if(ip->type == T_DIR){
iunlockput(ip);
- commit_trans();
+ end_op();
return -1;
}
@@ -148,7 +148,7 @@ sys_link(void)
iunlockput(dp);
iput(ip);
- commit_trans();
+ end_op();
return 0;
@@ -157,7 +157,7 @@ bad:
ip->nlink--;
iupdate(ip);
iunlockput(ip);
- commit_trans();
+ end_op();
return -1;
}
@@ -189,9 +189,9 @@ sys_unlink(void)
if(argstr(0, &path) < 0)
return -1;
- begin_trans();
+ begin_op();
if((dp = nameiparent(path, name)) == 0){
- commit_trans();
+ end_op();
return -1;
}
@@ -225,13 +225,13 @@ sys_unlink(void)
iupdate(ip);
iunlockput(ip);
- commit_trans();
+ end_op();
return 0;
bad:
iunlockput(dp);
- commit_trans();
+ end_op();
return -1;
}
@@ -291,23 +291,23 @@ sys_open(void)
if(argstr(0, &path) < 0 || argint(1, &omode) < 0)
return -1;
- begin_trans();
+ begin_op();
if(omode & O_CREATE){
ip = create(path, T_FILE, 0, 0);
if(ip == 0){
- commit_trans();
+ end_op();
return -1;
}
} else {
if((ip = namei(path)) == 0){
- commit_trans();
+ end_op();
return -1;
}
ilock(ip);
if(ip->type == T_DIR && omode != O_RDONLY){
iunlockput(ip);
- commit_trans();
+ end_op();
return -1;
}
}
@@ -316,11 +316,11 @@ sys_open(void)
if(f)
fileclose(f);
iunlockput(ip);
- commit_trans();
+ end_op();
return -1;
}
iunlock(ip);
- commit_trans();
+ end_op();
f->type = FD_INODE;
f->ip = ip;
@@ -336,13 +336,13 @@ sys_mkdir(void)
char *path;
struct inode *ip;
- begin_trans();
+ begin_op();
if(argstr(0, &path) < 0 || (ip = create(path, T_DIR, 0, 0)) == 0){
- commit_trans();
+ end_op();
return -1;
}
iunlockput(ip);
- commit_trans();
+ end_op();
return 0;
}
@@ -354,16 +354,16 @@ sys_mknod(void)
int len;
int major, minor;
- begin_trans();
+ begin_op();
if((len=argstr(0, &path)) < 0 ||
argint(1, &major) < 0 ||
argint(2, &minor) < 0 ||
(ip = create(path, T_DEV, major, minor)) == 0){
- commit_trans();
+ end_op();
return -1;
}
iunlockput(ip);
- commit_trans();
+ end_op();
return 0;
}
@@ -373,20 +373,20 @@ sys_chdir(void)
char *path;
struct inode *ip;
- begin_trans();
+ begin_op();
if(argstr(0, &path) < 0 || (ip = namei(path)) == 0){
- commit_trans();
+ end_op();
return -1;
}
ilock(ip);
if(ip->type != T_DIR){
iunlockput(ip);
- commit_trans();
+ end_op();
return -1;
}
iunlock(ip);
iput(proc->cwd);
- commit_trans();
+ end_op();
proc->cwd = ip;
return 0;
}