libvmon: Revert "libvmon: assume short positive reads found EOF"

This reverts commit 9f564cf8df6ef5fcba37082ba8013d6175955125.

Experimenting with smaller initial seq_file buffers in the kernel
has exposed this actually breaks, which contradicts my
expectations for proc files established back in the /proc/mdstat
racy incremental parsing corrupting the output days.

I'm seeing /proc/$pid/task/$pid/children spit out short reads
when the seq_file size is smaller than the amount of output.
Userspace's read() call can provide a large buffer, and if
seq_file's is smaller than the children output, it'll split the
children output instead of enlarging the seq_file buf to the
read() buffers bounds.

1 files changed, 0 insertions, 30 deletions

diff --git a/src/libvmon/vmon.c b/src/libvmon/vmon.c
index ec33b2d..a8e2121 100644
--- a/src/libvmon/vmon.c
+++ b/src/libvmon/vmon.c
@@ -145,12 +145,6 @@ static int load_contents_fd(vmon_t *vmon, vmon_char_array_t *array, int fd, vmon
 		memcmpcpy(&array->array[total], vmon->buf, len, changed, changed_pos);
 
 		total += len;
-
-		/* assume short read found EOF */
-		if (len < sizeof(vmon->buf)) {
-			len = 0;
-			break;
-		}
 	}
 
 	/* if we read something or didn't encounter an error, store the new total */
@@ -356,10 +350,6 @@ static sample_ret_t proc_sample_stat(vmon_t *vmon, vmon_proc_t *proc, vmon_proc_
 					goto _out; /* this saves us the EOF read syscall */
 			}
 		}
-
-		/* assume short read found EOF */
-		if (len < sizeof(vmon->buf))
-			break;
 	}
 
 _out:
@@ -449,10 +439,6 @@ static int proc_follow_children(vmon_t *vmon, vmon_proc_t *proc, vmon_proc_follo
 					assert(0);
 			}
 		}
-
-		/* assume short read found EOF */
-		if (len < sizeof(vmon->buf))
-			break;
 	}
 
 	/* look for children which seem to no longer exist (found by stale generation numbers) and queue them for unmonitoring, flag this as a children change too */
@@ -815,10 +801,6 @@ static sample_ret_t proc_sample_vm(vmon_t *vmon, vmon_proc_t *proc, vmon_proc_vm
 					goto _out; /* this saves us the EOF read syscall */
 			}
 		}
-
-		/* assume short read found EOF */
-		if (len < sizeof(vmon->buf))
-			break;
 	}
 
 _out:
@@ -876,10 +858,6 @@ static sample_ret_t proc_sample_io(vmon_t *vmon, vmon_proc_t *proc, vmon_proc_io
 					goto _out; /* this saves us the EOF read syscall */
 			}
 		}
-
-		/* assume short read found EOF */
-		if (len < sizeof(vmon->buf))
-			break;
 	}
 
 _out:
@@ -943,10 +921,6 @@ static sample_ret_t sys_sample_stat(vmon_t *vmon, vmon_sys_stat_t **store)
 					goto _out; /* this saves us the EOF read syscall */
 			}
 		}
-
-		/* assume short read found EOF */
-		if (len < sizeof(vmon->buf))
-			break;
 	}
 
 _out:
@@ -997,10 +971,6 @@ static sample_ret_t sys_sample_vm(vmon_t *vmon, vmon_sys_vm_t **store)
 					goto _out; /* this saves us the EOF read syscall */
 			}
 		}
-
-		/* assume short read found EOF */
-		if (len < sizeof(vmon->buf))
-			break;
 	}
 
 _out: