From 97281be7bb92ca1c1c5f089b1242cf6e673688ee Mon Sep 17 00:00:00 2001
From: Vito Caputo <vcaputo@pengaru.com>
Date: Mon, 16 Sep 2024 23:07:30 -0700
Subject: 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.
---
src/libvmon/vmon.c | 30 ------------------------------
1 file changed, 30 deletions(-)
(limited to 'src')
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:
--
cgit v1.2.3